The nice thing about terragen 2 is that you can very easily slowly ease yourself into the math parts. By default tg2 should choose and help you have settings that create realistic renders. theres also plenty of tools to make it so you barely have to worry about the math behind it, and it's very easy to do nice renders without ever touching the node network. Then as you find you want more control you can learn whatever you need to do what you want, slowly building up knowledge.
Also theres always people here on the forums who are very good at creating crazy function based terrains that amaze me, and i'm sure they can help you some. may post tgc (terragen clips) which basically hold all that function based work they did, and easily plug it into your scenes.
