College football overtime is a possession contest.

How overtime works

1. If the score is tied after regulation, overtime begins with a coin toss.
2. In the first overtime, each team gets one possession series, usually starting at the opponent's 25-yard line.
3. If the teams remain tied after both possessions, another overtime period is played.
4. From the second overtime, any touchdown must be followed by a 2-point conversion attempt.
5. From the third overtime, teams no longer run full possessions. They alternate 2-point plays until one team leads after matched attempts.

Both teams get a chance

The first overtime is built around fairness of opportunity. One team cannot end the game merely by scoring first on its opening series. The other team gets its own possession unless the rules or a defensive score create a completed result under the overtime format.

How a team's opportunity ends

A possession series is not guaranteed to last a fixed number of plays. It continues while the offense keeps the ball and can earn a new first down, but it ends when the team scores, fails to make the line to gain on fourth down, or loses possession. A defense can intercept a pass or recover a fumble and return the ball for points. If the defense gains possession without scoring, the opponent's offensive series is over; the ball is not simply returned so that drive can continue.

The team taking the second series knows the result it must match or beat. If the first team kicks a field goal, the second team can win with a touchdown, continue the game with a matching field goal, or lose by failing to score. If the first team scores a touchdown, the second team generally needs a touchdown plus the appropriate try to answer it.

Touchdowns require 2-point tries

If the game reaches a second overtime, teams that score touchdowns must attempt a 2-point conversion. The point-after kick is no longer available after those touchdowns, so coaching decisions become more direct and the game moves toward resolution faster.

The format becomes a 2-point shootout

Starting with the third overtime, the teams alternate 2-point conversion plays instead of starting new drives at the 25-yard line. Each side gets a matching attempt, and play continues until one team succeeds while the other fails in the same round.

Why the first score may not decide it

Each overtime is judged after the teams have received matching opportunities. In the first two overtimes, that normally means comparing the results of two possession series. From the third overtime onward, it means comparing one 2-point play by each team. If both teams score the same number of points in a round, another round is required. If one succeeds and the other fails, the game ends with the resulting difference.

Possession order still matters strategically. The team on defense first can learn whether its offense later needs any score, a field goal, a touchdown, or a particular try result. The team on offense first has the chance to put immediate pressure on its opponent. The coin-toss decision affects that order but does not remove the matched-opportunity structure.

Details fans miss most

• No game clock drive: overtime periods are not normal timed quarters.
• Timeouts reset: regulation timeouts do not carry over. Each team has one timeout in the first and second overtimes; beginning with the third overtime, each team has one timeout available for the remainder of the game rather than one in every shootout round.
• Defense can score: turnovers remain live enough to create game-changing defensive points under the overtime rules.
• Strategy favors defense second: many teams want to know what they need before taking their own possession.

"It is just like NFL overtime"

It is not. NFL overtime keeps more of the normal game structure, including field position and clock pressure. College overtime starts from a fixed field position and eventually turns into alternating conversion plays.

Source material

• NCAA - How college football overtime works
• NCAA Football Rules of the Game