I just installed wordpress for the first time recently and didn't like how the whole post showed up on the home page.
I discovered you can use the "Insert More" tag. In the visual editor it is the 3rd or 4th button from the left and looks like two rectangles with a dotted line going between them... or in the html editor you can just write the code as follows
So say your post is 12 paragraphs long... just put the <!--more--> tag just after the first couple of sentences or maybe at the end of the first paragraph. Then on your home page and category pages only the part before the more tag shows up followed by a link that says "read more" which goes to the actual post page.
Hope this helps