Open an image in PS.
Select the Type Tool.
Click on the area of the image you wish to place the type.
Change the type settings to suit your requirements.
(Holding down Shift will constrain proportions)
If you want to alter the type click Control T.
When happy with changes press Return.
In the Layer Palette, drag the Type Layer below the Image Layer.
Hold down Alt key and move the curser so that it is on the line between Layer 1 and Layer 2.
It changes into a little arrow with a square next to it.
You can use the move tool to change the placement of the type or the masked image.