Change CSS of a menu...

Perhaps It's a too newbie question but forget me but I don't manage CSS and I'm new to drupal. I'm using the Amity Island theme and I creating 3 menus to place in the bottom in blocks: User 4, User 5 and User 6. When I place them they appear, but the font of the title and the links they appear too big and also in bold...so the menu looks very ugly. how can I change this to create a smaller and nicer menu? (I can manage BASIC Css as font-family, and that sort)
Thanks!
mateo