Gimp.

I have been trying to create a watermark for about a month now. Apparently, it's easy.
But I am a Luddite. Computers detest me.
At the age of 7 I tried to fix my Tonka fire engine but only succeeded in superglueing my jersey to my arms, and my hands to said fire engine. I should have known then that I would never......ever.....be technical.

So, help me. For the love of God, help me.

(I need to export a transparency as a PNG from Gimp but it won't give me the option to save it as a PNG.)