public preview of privat posts

hey!

i’m looking for help or a plugin for showing a preview of all my posts. there should be a “read more” link or something like that after the short public preview.
if the post is privat there should appear a “you need to login to read this post” message.

so everybody can read a short preview of the posts, but just registered people can read the full posts!

i hope you know what i mean and can help me!?
i’m new to wordpress and all hits searching for it confused me more and more ??