I use Pixlr as well, and I know about the layout of the program, like mighty balto said, they ARE like clear sheets, I suggest if you can't see the little box/window with the title 'layers' on it, go to the top options panel, click veiw and click layers, but if you DO want to blend to create a 'graphic' as you see in others' galleries, open a background image, and copy and paste other photos in, in between each one, change the 'opacity' of the layer, to give it that translucent look then use the select and move tools to move it around, then if you want to blur the edges, take the (i use the biggest soft brush from the tools section) soft tool and erase the edges of the layer you just pasted, (don't worry, the background layer will NOT be affected) and continue with the process, moving around the images as you please if this didn't help with your issue, I could always help you out with something specific if you PM me for more info on Pixlr.com hope it helped you out!

Paint.NET is very organized with it's layers and so is Gimp if that's what you need. I know how confusing layers can be and the only way to get good at using them is just to get more familiar with your tools.

This depends on what program do you use. You can seach for some tutorials on deviantart. I can help you with photoshop too.

It is pretty simple, once you get the hang of it.
I've never used your programs, but I'll try to help.
What you need first is various images, put them all on the same image as seperate layers. Then adjust the opacity on each layer (or whatever layers you choose), to make it slightly transparent. Then you need a sort of faded eraser brush (if you want to merge them) to get rid of the straight lines and make it seem to be fading into the other image. then put them together in any way you like.
Also, if you are just starting out, try to use images with similar colours. Eg I made a Stampede image from the Lion King, and they were all sort of brownish, because they were from the same scene. As you get better, you will be able to mix all the colours. If you have any questions just ask.
Hope this helps

You should look into downloading GIMP just to save you the hassle of having to use paint, and then having to go to the internet to use an online editor.

Anyway, layers is the only way to achieve the effect you're looking for. And really, layers are very simple to learn; I never found them hard myself. Layers are just like a stack of clear plastic sheets, like a cel on background for example.

To get the effect your looking for, lower the opacity of the desired layer.