system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is creatine monohydrate and what does it do to the body?
gpt
Creatine is used to synthesize ATP, which is responsible for allowing your muscles to contract.  When you supplement your diet with creatine monohydrate, you increase the quantity of creatine in your muscles, which allows you to replenish ATP, which can lead to increased work capacity during a workout. 

Creatine does not need to be ingested at any particular time (like caffeine, which has a limited window before it wears off).  Creatine needs to be taken regularly to allow build-up in the muscles.  The recommended dose as a daily supplement is 5 grams.  Taking more than that hasn't been shown to provide any extra benefit.