formatting in weaver and twenty ten

I use weaver theme which is under twenty ten theme, and I need to change the format of the text only for some parts of it. For example, when I make a list, the distance between the lines is too big. When I have a text with different paragraphs is the same distance in between but this is ok, as it looks well.

Is there any solution to change the formatting only for a specific part of the body text?

In case that there is an option for changing the whole formatting please enlist it too. My skills in working with codes is near beginner level so please try to make it as simple as possible for me.

Thank you very much in advance for support!