I suggest you check out Scenic Express. They carry Woodland Scenics along with many others. Mostly from Europe. They offer many highly detailed scenic mats that can be placed readily right on the layout and glued in place. Check out the Martin Welburg line on there. Don’t expect any of this to be an inexpensive part of the hobby. Basic ground cover can be done at a reasonable cost as well as some of the ground foams. You start getting into detailed bushes and such the cost goes up.
You can also just use dirt from your back yard. Dry it out good and sift it. I use chopped up fall leaves done in a blender for anything resembling woods. The benefit of modeling the fall. All free. Just your time.
Lately I’ve found usable things on Amazon. Check out Wargaming Supplies.
A good investment starting out. Is one of Dave Friary’s books on scenery. Plenty of tips to get the look you want.