1. to (slightly) tear (That's the literal meaning. The main use of it is for muscles and tendons that are not completely torn, but there's a tear there. Besides this context, it's not common in this sense.)
2. to touch on a topic ("ein Thema anreißen" - pretty much ONLY used in contexts of conversations or presentations. If you're alone by yourself and you decide to look into something, that is NOT "anreißen".)