How do you cut off Word-Press posts so that only a part of it shows up when looking at your overall blog?

So I have a blog on WordPress but the thing is that my posts tend to be fairly long. Is there a bit of code I can put in so that maybe only a paragraph shows up before a link that says "Read the full post" or equivilant? I used to do this for LJ back in the day but I have no clue with WordPress.