How to transfer www.ads-software.com site back to wordpress.com

I’m very dumb when it comes to this kind of stuff so please help me out in laymans terms.

I want to cancel my hosting and move my www.ads-software.com website back to wordpress.com.

I originally started out on wordpress.com before I bought the domain name and found a host, so will it just show up as wordpress.com automatically after I cancel my hosting, or do I have to transfer it all over myself?

Should I back up all my posts before just in case?

Also, can I still keep my domain name and be on wordpress.com?