Nice to have you on the forum. Be sure to introduce yourself in the "Welcome Lounge" so we may give you a proper hello.
The Garter Snake Lounge

New snakes can go awhile before eating. It could take a few days to a few weeks. What species of garter do you have? What part of the country are you in? Knowing the species will also help us give advice on the feeding issue. A photo would be great