an easy way is to use photoshop;
new document - make sure the background is transparent > erase the edges
or
new transparent doc. > use the round rectangle shape (make sure it is on "path" not fill) and find your selection > make selection with the path > erase the outside.
I was confused for a long time about how to use the pen tool. It's definitely difficult for beginners but once you work it out, it changes everything. Get a good book or read some tuts and stuff, it's very much worth it.