Difference between various cmdlts avilable for site collection

Hi,

I am very new to sharepoint and I am a bit confused with the various options avialable for dealing with Site collection backup and restore kind of operation. Can any help me understand which one to use and when. Or what is the specific purpose of using each of them.

I am basically confused with:

1) stsadm backup and restore

2) Backup-SPSite and Restore-SPSite

3) Move-SPSite 

4)Copy-SPSite

5) SPSite Import and Export

Thanks,

Bhawna