Okay well if you are looking to get into plants, u should stay away from Petco/Petsmart. try and find a local store that specializes in fish. U might have to drive a little but it'll beat Petco. That light u got there won't do you much good. You could try to get some Java fern or Anubius tied to a decoration going but it might not turn out well.
Substrate is what the stuff you have at the bottom of your tank. right now you have gravel. Gravel has no nutrients in it and is not capable of sustaining plant life by itself.
you could however buy a better light, and keep some nice plants in pots. Are you willing to spend some cash on a better light? Aquatic life makes a great t-5 duel light for 137 bucks.
if you purchase that light, you could do some other plants that will do well.