Here are some ways it can be used:
* "Buck up, you'll get through this!" (Encouraging someone who's facing a difficult situation)
* "He seemed a bit down, so I tried to buck him up." (Helping someone feel better)
* "The team's morale was low, but the coach's speech bucked them up." (Motivating someone to regain enthusiasm)
It's worth noting that "buck up" can also be used in a more literal sense, meaning to put on a coat or jacket. However, this usage is less common than the metaphorical meaning of cheering up.