WASHINGTON » Ruben Gallego arrived here Sunday night, crashed on a friend’s air mattress and went apartment-hunting Monday morning, only to discover it costs $1,900 to rent a 400-square-foot studio on Capitol Hill. He spent that afternoon working from his laptop on the second floor of a Dunkin’ Donuts, talking on his cellphone while pacing about in his stocking feet.

Such is the humbling life of a newly elected member of Congress.

Gallego, 34, who grew up poor in Chicago, worked his way through Harvard cleaning bathrooms and later fought as a Marine reservist in Iraq, is now Rep.-elect Gallego, D-Ariz., one of 58 House newcomers suddenly confronting life in Washington. On Wednesday, they descend on Capitol Hill for a congressional rite of passage: freshman orientation.

With 41 Republicans and 17 Democrats, including 11 women, five African-Americans, three Hispanics and two Asian-Americans, the House freshman class of 2015 is a slice of America. There are 11 veterans, two pastors, a Virginia Volvo dealer who was President Barack Obama’s ambassador to Switzerland, a former CIA operative from Texas who worked undercover in Pakistan, and a Long Island lawyer who succeeds Eric Cantor as Congress’ sole Jewish Republican.

They are about to learn that going to Congress is a lot like going to college.

There are housing arrangements to make ("I look forward to talking to other freshmen to see if there is anyone I can room with," said Carlos Curbelo, R-Fla.), friendships to cultivate and new rules to learn. There is a pecking order, rooted in seniority: In the lottery for office space, freshmen pick last.

And there are class elections.

"I’m running for ‘the elected’ — it’s the one where you sit with the leadership," said Mimi Walters, R-Calif., searching for the name of the Elected Leadership Committee, which controls decisions for the Republican caucus. "I’ve been sending letters to everyone, to freshman class members, to have them vote for me."

There is no instruction manual for serving in Congress, but Rep. Kevin McCarthy, R-Calif., the House majority leader, did send his newly elected Republican colleagues a 125-page spiral-bound document called "Hit the Ground Running." It offers advice on everything, including hiring a chief of staff and opening district offices, and it has a helpful list of orientation "dos and don’ts."

As in: "Do think about what committees you are interested in." But: "Don’t talk to the press about committee assignments."

Too late! Walters has already confessed she is gunning for a spot on the Energy and Commerce Committee, though she knows it is a long shot for a freshman. "Why not shoot for the stars?" she said.

Freshman lawmakers invariably have compelling stories to tell. Gallego, a son of immigrants from Colombia and Mexico, was an assistant machine-gunner with Lima Company, an Ohio-based infantry reserve unit that suffered devastating and highly publicized casualties in Iraq.

Curbelo’s parents are Cuban exiles. Now 34, he carried around a copy of Newt Gingrich’s "Contract With America" when he was 14. "I hope that doesn’t make me sound too nerdy," he said.

Will Hurd, R-Texas, is an African-American representing a majority Latino district — and a former undercover operative with the CIA. He is already polishing his sound bites. "If I can navigate the back alleys of Pakistan," he said, reprising a line he often uses, "I think I can navigate across the aisle in Washington, D.C."

For new senators, whose orientation also begins Wednesday, the transition is sometimes less jarring; some come straight from the House.

Of 12 Senate freshmen (including Dan Sullivan, a Republican whose victory in Alaska over the incumbent Democrat, Mark Begich, was reported by The Associated Press early Wednesday), five — the Republicans Shelley Moore Capito of West Virginia, Tom Cotton of Arkansas, Cory Gardner of Colorado and James Lankford of Oklahoma, and a Democrat, Gary Peters of Michigan — already serve in the House. A sixth, Ben Sasse of Nebraska, who worked for President George W. Bush, once ran a congressional office.

Congressional orientation sessions are bipartisan, but Peters might feel a little lonely: He is the sole freshman Senate Democrat. "It’s a good opportunity to get to know members in both parties," he said. "In my case, it won’t take me long to get to know the other members of my own party."

Rep. Candice S. Miller, R-Mich., chairwoman of the Committee on House Administration, oversees the sessions in the House. There will be lessons on ethics rules, how to vote using electronic swipe cards and the all-important class photo, taken on the Capitol steps.

Miller’s own orientation 12 years ago was "such a blur, with so much paperwork," that she is now offering an alternative: iPads (with the cost deducted from new members’ budgets) fully loaded with all the information a rookie lawmaker needs.

Still, they will be in for some shocks. New lawmakers inherit their predecessors’ equipment (including their sometimes antiquated computers), but not their budgets, which tend to grow with seniority. Don Beyer, the Virginia Volvo dealer, replaces a fellow Democrat, James P. Moran.

"We’re expecting a budget of $1.2 million," Beyer said. "That’s two-thirds" of Moran’s budget.

As for office space, Beyer figured the worst spot would be the basement of Longworth, one of three House office buildings in the Capitol complex. Then he learned of an even less desirable location: the fifth floor of the Cannon Building, carved out from a former attic that can be reached only by a few elevators.

Beyer, though, has it easy. He lives right across the Potomac in Northern Virginia and does not have to move. For those who do, Washington can be daunting.

Curbelo, a father of two young daughters, said he is "scared about time away from my girls." So is Lee M. Zeldin, a New York state senator and father of 8-year-old twins who is soon to be the sole Jewish Republican in Congress. The fear, he said, is "you’ll end up with a fractured home front."

Walters, a 52-year-old mother of four, has spent the past decade in the California Legislature. Her youngest child just left for college; she is trying to downsize, while going bicoastal. "My husband and I are trying to sell our house, I have to move out of my apartment in Sacramento, I have to resign and get settled in D.C.," she said. "I feel like I have a lot on my plate."

Gallego, who served in the Arizona Legislature, is trying to put such worries aside. He abandoned his apartment search on Monday in favor of angling for committee assignments.

"Yes, I understand, thank you for your consideration," he could be heard saying, as he paced about the Dunkin’ Donuts, sans suit jacket and shoes. "Whatever you need. I’ll be a good caucus member."

He was on his fourth cup of coffee, yet seemed a little tired. ("What day is today? Is today Tuesday?" he asked.) He had skipped breakfast; lunch was late: a 6-inch meatball sandwich from Subway. "Can you not write that?" the future congressman pleaded. "My wife’s going to kill me! I’m supposed to watch what I eat."

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