Creating a gradient within a shape

I'm pretty adept at making webpages but Photoshop is all new to me. I watched a video tutorial and it really didn't address this (or I missed it). If I open a new project and add a layer, then create a rounded rectangle, is there a way to fill just that rounded rectangle with a gradient. I keep getting a message that the layer is not directly editable or something. I need to just play with the thing, I'm sure - eventually I'd porbably sort it all out. But I got a job creating a web page for a mortgage company and I wanted some custom buttons with a gradient fill - I'm on somewhat of a deadline. Any help would be greatly appreciated...

K, click the "rectangle tool (U)" then check in the top of photoshop just below the bar when you have, File Edit...

There are 3 buttons, click the first one "Shape layers", draw your rectangle and the double click your layer and a window with lots of check boxes, check the one that says "Gradient Overlay" and play around....

Also, you may be getting this error message ..err warning, because in your layers you do not have the correct layer selected.

To edit a layer you need to first select it, simply left clicking on the correct layer in the layers window will do this. You will know it is selected because you'll get the paint brush next to the layer.

Then to select your rectangle, if it's the only content in the layer you can Ctrl+left click on the layer in the layers window.