If your image is simple, you can just use the magic wand. If it has a complex background and you are hoping to cut out a particular element of the image, you'll want to use the Lasso tool. With this tool, you'll be tracing around the object you want to cut out manually. A great example of this type of use is cutting out a person completely from an image and pasting their likeness into an entirely different image. This is very doable, but it requires some skill and effort. You're going to need to take your time the first few times you tackle this process, but once you get the hang of it, it should become second nature.
Two lasso tool options
The *freehand* lasso tool can be used to draw around an area with your mouse. It can be difficult to do this with precision using a mouse. It's much easier to do if you're using a pen-and-tablet device (although of course most people do not use those). You may instead want to use the *polygonal* lasso tool. With the polygonal tool, click and click again and keep laying down straight lines, with Pixlr connecting your points along the way. In this way, you'll be able to have finer control over what you're cutting out. Your ultimate goal is to draw a point-by-point area that closes in on itself at the end — you end up where you started and have your area selected.