transfering posts

Can’t you just use the same database for the new one?

no.. its on different domains.. but what if i transfer the database contents? yes? no?

Can’t you do a back up of the one backup, and then create a new database on the new site with the same name, and then restore it

https://codex.www.ads-software.com/WordPress_Backups#Database_Backup_Instructions

i already set up the database. should i just upload the back up and rename it?

You can backup only the DATA from the first (old) WP install and import it into the new one. Make sure the two WP installs use the same version. Once I’ve moved a few posts from one blog to another – the method is the same even if you move all the posts.
Here is a tutorial I’ve posted about it.

I believe this is what you’re looking for.

https://www.tamba2.org.uk/wordpress/move/