Creating partial entry on the main page

I would like to create a partial entry on the main page, maybe like the first 500 characters and if they would like to read more they would have to go to the actual page.

I have just started using wordpress so consider me a noob.

Also there seems to be a big gap between post

from the footer of the post and the header of the next, when viewing the source, I see all this XML in between each post which is hideen but I guess creates a gape between each entry

also another issue I found is inserting javascripts create returns on the page, similar to an extra page break

but my main concern now, is just creating a partial entry on the main page and if you would like to read more click here or read more type