First off, Welcome to the Guild, The Mappiest Place on the Web
Secondly, How to make mountains will depend on the style you want them in. With your weapons of choice you should be able to find all kinds of tuts in the Tutorials section for them. I would suggest you look through the Finished Maps forum first and look for a style that you want, then see if there is a mention of the WIP (Work In Progress) thread about it. Most often that is where the ideas , or mention of the tuts, where the techniques used came from. Follow those to the tuts and have fun.