1:
Use google images to search for "ball python". Ball pythons have a pretty distinct look.
2:
If so, check out this CARE SHEET. This will get you 90% of the way to knowing how to care for a ball python. The other 10% is experience.
3:
If not, and if you have a camera, take a picture of the snake and post it here, so we can help identify the species. It is important to know what species it is, because it may have different care requirements.
Extra info on ball pythons
A glass cage with a locking mesh top that is 32''x12''x12'' is large enough for any 3 foot long snake. Some snakes will outgrow that, others won't. Some that do outgrow it will take longer, and that size will be large enough for a ball python for quite some time.
Read the care sheet. Come here and ask questions (you probably will have some). Taking care of a ball python isn't hard, but it's always nice to have reassuring answers to questions you may have.