Washington (CNN) With the Senate falling short of the votes needed for a funding proposal, the United States federal government officially shut down Friday at midnight.

Lawmakers had a similar deadline last month, but they passed a continuing resolution December 21 to keep the federal government funded for another month.

Democrats had been pushing a solution for recipients of the Deferred Action for Childhood Arrivals program and insisted that it be addressed before the Friday deadline -- and the two parties were unable to reach an agreement.

The House voted Thursday night to avert a government shutdown, sending the bill on to the Senate, where it failed, 50-49

Shortly before the House vote, the Freedom Caucus said a majority of its members would vote to support a stopgap spending measure, a key sign that holdout conservatives who had been undecided earlier had come on board.

The Senate measure needed 60 votes to pass the chamber to break a filibuster, which meant that Republican leaders needed as many as more than a dozen Democrats.

The shutdown, however, doesn't mean every federally funded agency, program and service will grind to a halt. Whoever works for agencies and departments that are considered nonessential, including agencies that pay out small business loans and process passport requests, will cease to work until Congress is able to agree on a bill for the federal budget.

The employees in these departments will be placed on "furlough." In previous shutdowns, everyone who stayed home was paid retroactively after an agreement was reached in Washington.

At the peak of the 2013 government shutdown, about 850,000 employees were furloughed per day, according to the Office of Management and Budget.

But what is considered essential and nonessential?

President Donald Trump tweeted last week, "The Dems will threaten 'shutdown,' but what they are really doing is shutting down our military, at a time we need it most."

And on Tuesday he tweeted, "The Democrats want to shut down the Government over Amnesty for all and Border Security. The biggest loser will be our rapidly rebuilding Military, at a time we need it more than ever. We need a merit based system of immigration, and we need it now! No more dangerous Lottery."

The Democrats want to shut down the Government over Amnesty for all and Border Security. The biggest loser will be our rapidly rebuilding Military, at a time we need it more than ever. We need a merit based system of immigration, and we need it now! No more dangerous Lottery. — Donald J. Trump (@realDonaldTrump) January 16, 2018

During a shutdown, the military is considered essential and would still report for duty. However, the troops -- including those in combat -- will potentially not be paid during a shutdown. In addition, many civilian Department of Defense employees will not be working during a shutdown, including instructors at military academies and maintenance contractors.

If the shutdown goes on for weeks, about 1.3 million active-duty military will be expected to work potentially without pay. The military is currently paid through February 1.

Special counsel Robert Mueller's team will continue to operate, a Justice Department spokesperson told CNN

"All employees with the Special Counsel's Office are considered exempt and would continue their operations in the case of a lapse in appropriations," the spokesperson said.

But if you had plans for a vacation to visit any national parks, zoos or museums, those will be closed.

The shutdown will also affect the Bureau of Alcohol, Tobacco, Firearms and Explosives, meaning if you wanted a gun permit, you'll have to wait until the shutdown is over.

Essential services, such as Social Security, air traffic control and the Transportation Security Administration, will continue to be funded even if some employees of those agencies are not.

And the US Postal Service won't stop serving residents -- you'll still get your mail.

Members of Congress will continue to receive paychecks because it's written into law.

In 2013, the shutdown especially affected residents of Washington. But this time around, Mayor Muriel Bowser vowed that services in the city will continue, unlike last time.

"Washington, DC, is open," Bowser said in a statement published Friday. "DC government will continue to provide services to our residents, the services they expect and deserve, uninterrupted."

She also said the city plans to help the federal government maintain the National Mall.

"I've called on my agencies, where we are able, to step in for the federal government," she said during the press conference. "The National Mall is operated by the National Park Service, and there are many other National Service Park properties throughout Washington, DC ... we will step in and ensure litter and trash are picked up along the National Mall to keep nation's front yard clean of debris."

This story has been updated to reflect new information from the District of Columbia.