Hi Kathy! Welcome to TDA! My name is Rod!
There's a whole lot to learn and the lovely members of TDA have made a lot of awesome tutorials on getting started!
Katharos has a great on understanding composition.
Holster has an amazing tutorial on coloring screencaps which is an important base to graphics making.
Persephone also has a nice bag of tips to get you started. I would start exploring the technique tutorial section because it has a lot of nice tips and tricks on how to started on graphic making.
Also, it never hurts to experiment, just start getting in there and try playing with blend modes and anything else you can get your hands on. There is also the Artist Q&A where artists have made themselves available to answer your questions. I hope to see you around!