Welcome to the hobby. Since you're new, I would recommend going to a local hobby shop and buying (or ordering if the store doesn't have it in stock) Woodland Scenics' "Scenery Manual." It's full of "how to's," drawings, and photos for doing all kinds of scenery. Obviously, they plug their own products, but they are also the best known name in model scenery.
While you are at the store, look at the wide variety of scenery products that are available. You'll find everything from ground foam for grasses and weeds to ready-made trees and shrubs.
There are also several books available on the subject. One of the best known is Dave Frary's "How to Build Realistic Model Railroad Scenery." It's a bit expensive but well worth the money. It's also available from a lot of public libraries.
I'm sure you'll get a lot of other good advice from the good folks here on The Gauge.
One thing about doing your own scenery: it can be an "art form," but you don't have to be an artist to do it. It's much easier than it appears.
