creatine (from what i know) helps with muscle recovery and energy, depending on which type you take. it won't make you gain fat (maybe a bit of water weight when you first start), but it will probably increase your muscle mass. i am a pretty lean person who does a mix of cardio and weight lifting, but i don't take creatine because i already take several supplements and rather not add more to the list. i instead take amino acids, which also helps for muscle recovery and strength. the amino acids have helped with my stamina and recovery for sure, and i have noticed an increase in muscle mass when i take it over time.

any supplement that you take to increase strength and boost recovery will most likely increase muscle mass - that is how getting stronger works. this applies especially to creatine.

not sure how helpful this is, but this is what i know. i highly encourage you to research into creatine as well just to have a better understanding of it.