Nice to meet you Cirrus, and welcome to the site.
A. I'm assuming you mean a coven on here since you asked here. There are several covens that teach in different areas of witchcraft and paganism. You should make a list of magickal topics that interest you, and then find a coven that teaches or focuses on those subjects. It's not garunteed that you'll find one to meet your every exact need, but there will most likely be one out there that sparks your interest.
B. Spiraldance is right with the general "if it sounds impossible, it probably is" rule of thumb. Try some of the spells out to see if they work for you or not. Intent and belief does play a large part in casting spells, so take that into consideration when you practice. If you're still not sure which spell(s) to use, write your own. It will be specifically designed/customized for you, and will carry your own personal energy, which may increase its effectiveness.