You can define the properties of a layer by right-clicking on its Layer Tab and choosing Layer Properties from the menu, or by choosing Layer Properties from the Layers submenu under the Image menu.
Setting Layer Properties
By un-checking the Is Visible box you can hide the layer, making it not only invisible to the eye but treating it as if it did not exist at all. An invisible layer will not affect a printed image, and if the image is flattened or saved for publishing, the information on that layer will not appear in the final image. Checking Is Visible will turn the layer back on.
The Opacity slider defines the opacity/translucency of the entire layer. The less opaque the layer, the more the underlying layers show through it.
If you check Automatically Add Text as a Floating Object, your text will be laid over the image in a floating state that allows you to keep moving it, or re-opening it for editing, as long as you like, even after you have added other objects to the layer.