In photoshop open up you main image and the texture that you wish to work with. Set you tool to the move tool. Select the texture, hold down your left mouse button and drag it onto the top of the main image
Move Tool
Drag
Release the mouse button the texture will then either cover all the picture or part of it.. You can now close down the original texture image as you no longer need it.
Pull out the corners then click on the tick to resize the texture layer