I’ve tried to look this up and I know it has something to do with the alpha channel or something? But for some reason this one of things I just can’t seem to push through so if someone could show me how to do this (and then help me find my mommy) I’d appreciate it. 
Gimp novice here. I hope there are errors in my explanation, so an expert will come along to teach me too. 
Start by
Layer → Transparency → Add Alpha Channel
Once you have the alpha channel, two of the ways to make image regions transparent are the Eraser tool and, after selecting pixels (by color, region, etc.) using
RightClick → Edit → Clear
When I have transparent areas in an image I always Export as Gif – the only standard format I know that supports it.
PNGs support it, too. JPEGs, most definitely do not.
Septimus: Thanks. I think part of the problem I ran into looking this up was that what people usually want to do is just make part of an image transparent. I want to make the whole thing mostly transparent so I can use it as a watermark.
So is the obvious answer to select everything and . . . erase? Like with the eraser tool, or is there another method? It’s 8.5x11 (or close enough). I guess I could just zoom out though.
pulykamell: Thanks. That was another problem and reason I got very frustrated - tried to use the wrong file type.
I appreciate the link, but ummm, you did see the part about 21 layer modes right? I’m hoping I don’t need all 21.
This is somewhat off-topic, in that it doesn’t answer the OP’s question directly, but…
Here are some video tutorials for GIMP newbies.
What you’re looking for is Opacity. In the Layers palette there should be a slider to adjust opacity. For a watermark I’d go towards 30%.
I had a feeling. I had the same issue trying to make transparencies in Photoshop at first, and my transparent layer would always end up solid white when I saved it. That’s because I was saving it as a JPEG and JPEGs don’t support transparency. :smack: GIF or PNG? I think, but I’m not sure, that if you want partial transparency then PNG is the format you need to use. GIFs, as far as I know, only support one-bit (single color) full transparency (you can’t make things translucent with them.)
Correct and additionally nobody should ever be using GIF for anything in the year 2013 except making cute little looping movies for joke sites.
GIF is a terrible format, let’s all help it die quicker.
Thanks guys. So I should focus on the opacity layer? I guess I’m going to open the file, create a new layer and then try to figure it out from there? I’ll try to look at this tonight or tomorrow and see if I can get anywhere with it.
You’re right. No one can even pronounce it.
Unfortunately, the only other formats that support transparency are PNG, which has its own problems, and native file formats like PSD. Does GIMP have a native workfile format?
TIF also supports transparency. Whether it’s better than PNG or GIF, I couldn’t say, though.
It’s erratic, which is why I did not mention it.
So what’s the state of GIFs these days? My rule, learned about 15 years ago, was JPEGs for photographs, and GIFs for line drawings, graphics with a limited color palette and hard edges, that sort of thing. Rasterized text, logos, etc.
Have GIFs completely fallen out of favor for that use? JPEGs, because of the way they compress image information, suffer for graphics with hard edges and solid colors. What format is preferred for that these days. PNG? (ETA: I’m speaking in terms of web reproduction.)
PNG 100% replaces GIF for anything GIF used to do. Except silly animations on joke sites.
I’m not sure what “problems” PNG has that Amateur Barbarian was thinking of. The only “downside” (if you even call it that) is that there’s no such thing as an animated PNG. (Ok, technically there is-- but nothing supports it.)
There’s nothing wrong with JPEGs for photos. The good thing is you can use less harsh compression settings, as file size is no longer the issue it once was. A 200k background image on a website loads lightning fast, and JPEGs of 1MB or more are not unusual in some places, like Flickr or DeviantArt.
Yes, it is called “.xcf”. It contains the separate layers.
As for the OP, when you create a new image, you can choose to fill the image with Black, White, or Transparency. You might start with that, then add a Text layer (or a layer containing your logo) and then change the Opacity of that layer to something substantially less than 100%, as mentioned upthread.
Then, save it as a PNG.
I don’t think anyone is arguing against JPEGs, unless I’m misunderstanding. The problem is that JPEGs don’t support transparency, which the OP needs.
Erratic browser support, for quite a long time. I think that’s been eliminated but I still have more rendering and loading problems with PNGs than with any other brand.