Hi Ryan. A tear is when you pull or rip (something) apart or to pieces with force. For example it could be a piece of paper such as a letter. To shred something is to tear it into very small, fine pieces. In the example of a letter, you would shred it so tye address or headed paper of your company couldn't be recognised when putting the tiny pieces back together. A shredder (machine) performs this task. A rip more often refers to a rip in a curtain, in clothes (often trousers), or other material. It is often unintentional and is more negative; you would want to repair it or replace it.
Hope that helps :-)