Check out daoc.catacombs.com. There is a character builder there(use version 2, not 1.5) that should help you out. Basically, most casters have "non-spec" spell line(s) and "spec" line(s). You will get all the spells in the "non-spec", or baseline, regardless if you train in that spell line. You will only get "spec" spells if you train in that specific spec line. Also, your spells resist rate and effect are proportional to your spec level.
For example, say you are level 20, and cast a baseline damage spell that is level 20, and your spec level is 1 (you never trained in this spec line). Your damage would range from 0-75% of the base damage of the spell. If you had a 10 skill (50% specced), it would be 50-100% (I think). At level 15, you do 75-125%, and at 20 (fully specced), you do 100-125%. As you can see, training in a spec line will reduce the amount of variance in damage that you do. This also applies to healing spells, as the amount you heal also is adjusted by spec level.
Hope this helps