What do I do with Freighter and Supply Ships?

I have a couple of Freighter ships but I don't know what to do with them.  How do I use them?

I also have a Supply ship. I guess I just send it to a planet, but it needs to be a core world. Is that correct? What is a good strategy for using Supply ships?

Also, is there a way to get more Survey ships? I don't see it as an option to build.

 

Thanks!