Picture Transperency, How Do you do it with The GIMP 2

Hello, I was wondering, I trying to make a Signature in GIMP using The Phantom69's Guide, I've got everything (the backgrounds, brushes, tools). After I make my Back Ground, I get my Picture for the sig and It come with the white background so when I paste it, It comes out as a block with a picture in it. I was researching on how to fix this problem, and apparently you have to make it transperecy, so I look in The GIMP 2 and moved the mouse over to the eraser, and it said, ~Erase Things/Invisible things~ (Or atleast I thought It said that) and I click it But it doesnt have anything about it.
Here's what I mean/wants (tooken from Phantom69's guide):



See the Black and Grey Boxes near the Halo dude, thats what I want, a tool or something to erase parts in to those Grey And Black Boxes.

Thanks for any of your help!

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C'mon guy's, I know you know the answer!!

 

http://members.home.nl/m.weisbeek/gimp/#dialogs

I have never used GIMP, but I found a guide for it. See if it helps. Look at the layers information.

Hope it helps.

 

Ok Thank's, I have Been Able to do it now