Homegroups

Can someone please explain the concept of Homegroups.

I thought that if I had 2 Computers connected to the same homegroup, that I could transfer files from one to the other.

However I must be wrong on this, because I have my Laptop which says
"The Homegroup is not available because you are not connected to the Home Network".
My Desktop asked on W_!0 set up if I wanted to join a Home Network, and I said yes, but now it's trying to create one with a totallyu different password to the one I have written down. I have changed this to the one I thought I had from before, but my Laptop is not letting me view or change the password, as it says I'm not connected to the home network!

I can't seem to win here, so is there any way I can start again from scratch?

I have set the Laptop to "Leave the Homegroup", but now it says I can't reconnect because my laptop is connected to multiple networks! :mad:

Thanks

Homegroups