Can I just suggest that you absolutely forget about biomes if you can't make and use height-maps yet.
Step by step is the way to go.
A +---+---+ B
C +---+---+ D ---------x
imagine the +'s as the vertices of your mesh. Simply randomize the height of the corner verts (A,B,C,D), then average the mid-verts between these, with a little randomness as well. Keep doing this foreach mid-vert until all your verts are positioned in the z direction. You'll end up with a fairly natural looking terrain. There are all sorts of ways in which you can modify your height algorithm, using various noise and smoothing methods.
There's not really any math behind generating a simple terrain mesh. Not until you look at more complex methods, when you're after more interesting results. But you have to be comfortable with generating height maps first.