You picked the right section. Here's a link to the forum care sheet which might answer some of your questions.
Garters like to thermoregulate so giving them a hot and cool spot is best. Garters are very inquisitive and spend a lot of time watching their world. 100° is too hot for a hot spot, low 90's would be better.
I've found paper towels to be an invitation for hiding. A pellet type substrate usually deters the hiding for the most part. Providing a hide on the hot spot and the cold spot is best.
Your snake is probably spending more time out then you see. Hope this helps but feel free to post addition questions.

Garter Snake Forum - Garter Caresheet