There are as many model railway layouts as there are model railway enthusiasts, and then some! There are model railway builders who create replicas of real world track layouts that are perfect down to the tiniest detail. And there are others who make a model railway layout that only exists on the train table. Both ways are fine: there’s enough room for every design when it comes to model railroads.
There are a number of retailers selling accessories for every scale train layout. You can buy trees, buildings, automobiles, even people that are made for a certain scale model railway layout. You can even order custom made accessories built to your exact specifications.
But you can also build your own landscaping for your model railway layout, and there are some model railway hobbyists who wouldn’t have it any other way. You can, for instance, build your own berm on either side of the tracks using Styrofoam, a grater, glue, paint, and pieces of board to put it on. Did you know that you can create a realistic pond by cutting out wax paper and painting it? The smooth surface gives it a realistic look.
A pebble makes a fine mountainside boulder, and you can imitate cultivated fields with dry coffee grounds (smells nice, too!). You can even make your own trees using steel wool for the canopies and bits of wire for the trunk and branches. Realistic snow is not always easy to make. Some people use talc, and some people make snow that looks realistic, but actually forms a solid layer on the scenery. This, of course, produces less of a mess. To do this, you mist the scenery you want snow on with water, then sift small amounts of white gypsum cement over it. If you keep doing this in thin layers: mist/sprinkle/let dry several times, you can get a realistic looking snow scene.
The most important thing when building your model railway layout is not to be afraid to try something new. You may not be great at making papier mache mountains yet, but with practice you could become an expert.