could not use the gradient tool because the content of the layer is not directly editable

what is going on here? I haven't use photoshop that much, but I just recently started a new project, trying to design some buttons for a web page i'm making, and thats what it says when I try to use the gradient tool. Any way I can get around this? i dont know why its saying that.

you could be trying to use it on a vector layer, like a type layer or a shape layer.