some help with making tiles?

ok, I'm loving everything so far, but some things I don't get.

was trying to make my tiles background transparent.  I went into the tiles editor and gave it a background, set the blend mode (tried several things) and the alpha to different levels as well...  I cannot see how to save, all I see in the File menu is 'open existing' and 'create new'.  I thought maybe it would save the stuff anyhow. I closed the program and reopened my skin, it DID save...  but still no change to my actual tile on my desktop.

I messed around poking at things like this for a good hour yesterday...  but I'm really not getting it.

thanks for taking a look here.  would love a push in the right direction, I'm out of ideas.