Nice to have you on the forum. Be sure to introduce yourself in the "Welcome Lounge"
Welcome Lounge - Garter Snake Forum
It would be great to know what species/subspecies garter you're talking about. What part of the country do you live in. Any chance you can post a few photos of your snake?
Didymus was given some good advise.
Here's a link to the forum care sheet. It will help answer some question. Anything not covered feel free to ask on the forum.
Garter Snake Care Sheet - Caresheets