If I drop the glass toy, can I use it again?

You should look for any fractures or chips before using it again. Will the glass toy break if. 

I heat it or cool it?

The borosilicate glass endures high and cold temperatures. You can place it in the freezer or warm water without worrying about cracking or chipping. You should test the temperature before putting it directly in your genitals.

How should I clean the glass toy?

Water and soap will do fine. Glass is a non-porous material, meaning that it does not absorb any bacteria, making it body-safe, hygienic and easy to clean.