The Aero Library has two levels of content: Basic and Premium.
Every paid subscriber has access to library content– at the time this article was written, it was about 45 templates and about 40 procedures.
Subscribers who pay for the premium content have access to everything in the Aero Library, currently 103 templates and 93 procedures.
You can access the basic content while you're on your free trial by entering your credit card. You won't be charged until the end of your trial, but you will be able to use the library content. Trial accounts also come with 4 free templates already loaded into the Aero templates list.
You can search through the library to see what templates are premium and which are not.