As a beginner its important to find the materials that works for you. I started off with basic art painting used in school to make sure I was comfortable spending more on supplies. First find a easy painting to do like a sky just blue and white with a 1 inch brush, then do land black and brown also with the 1 inch brush
Once you that those 2 basic things do a simple trees with green and black to give it depth and constant. After you do the basic tree do branches you are on your way. At first it may seem like nothing but it will come along. I put it a side and look at it to make sure its what I want it to be. You can then move on the doing leaves on the tree branches using the same 1 inch brush turn it on it side, the colours I used are yellow, red to make orange black and green also to give the tree flavour.
Good luck, have fun.