How to install new SSL cert

I just brought up an e-commerce site and not sure how to switch to the new authentic SSL certificate from the self signed.

I noticed that Vmin has 2 files
~/ssl.cert
~/ssl.key

The cert people sent me these:

myserver.key <-- that is the real file name
www_domain_com.cer <--real "domain" omitted for this post
server.csr
xroot.crt

I am totally lost on how to set these up in this customers vhost account with virtualmin.

Thanks,
Max