1.Open a new image of whatever size.
2.Use the rectangle select tool and create your canvas.
3.Create a new layered named rectangle.
4.Fill the rectagle you selected with your color of choice on the new layer.
5.Create a new layer, name it gradient, (there should still be "ants" around your rectangle)
6. With the gradient layer selected, click your gradient tool.
7. Make sure the settings are on linear, change the options from "FG to BG" to "FG to Transparent"
8. Make your foreground color white.
9. While on your graident layer, use the graident tool and drage from the top middle of your image to wherever you wish, probably about 3/4 the way down. Hold CTRL to make sure the gradient is set straight.
10. go to SELECT, and click SELECT NONE.
11. Choose your gradient layer and lower the opacity to desired level.
*Optional Step* 12:create a new layer and add a noise or pattern and lower the opacity very low.
13. right click on the gradient layer (should be above the rectangle layer) and click merge down.
14. Your done
Hope I didnt miss a step, i suggest you just mess around with all the tools above to because you can create some really nice effects with gradients and noise/filters/patterns.