Help with Paint.net gradient tool

I downloaded Paint.net recently so I could do effects like gradients, but I can't get gradients to work. when I try to add one it replaces the image I'm trying to put the gradient over, and if I put someting over the gradient it replaces the gradient. I also can't get a linear gradient that doesn't cover the whole image. I'm trying to make tilesets specifically, and this is a problem. Also when I tried to use a 50% transparent white and fill a spot with the paint bucket, it filled the whole picture. Is there a way to stop this from happening?

Did you use the selection tool to "fence off" an area before editing it?

No, I didn't. It seems so obvious now. Thanks!

Shawnachu saves the day!

You can mess around with blending modes..

If you dont have them in paint.net try downloading plugins

As for the paint bucket tool: lower the tolerance. It's that bar at the top that says 50%; click and drag it to the left so it has a lower number.

Thanks. I have new problems though. How do I keep what's behind a transparent part without it ending up like the attachment? And how do I keep what's behind a gradient? The background just turns white, it isn't even transparent.

Use layers and paint on the layers. You won't affect whats on other layers and you can move em back and forth.

if you don't know where the layers are or can't see them, you can turn them on in the VIEW panel.

Layers are like layers.

You put one transparent screen over the top. draw on it, and it wont affect the one below.

Ah, I didn't think to layer. Thanks. I still can't figure out how to keep what's behind a gradient though.
EDIT: Just figured it out. You switch to transparency mode.
EDIT 2: The method I found only seems to work with white.