I think it is important to use the materials that you have on hand when you are first beginning as you may find that it is not for you, and there is nothing worse than spending your craft budget on materials that you won't use again.
A quick search on Pinterest or Youtube will yield a swathe of recipes for Gesso, texture paste, mod podge, paint sprays and more. Though sometimes it is actually cheaper to buy the product ready made rather than buying jugs of the ingredients, if you have everything on hand it makes sense to make your own pastes and sprays.
So let's begin on our mixed media exploration. Lesson 1: Gesso
You can get the free image from Gecko Galz here