This is an alternative to using the Clone Stamp Tool and is more suitable for large areas. It is more flexible because the cloned area can be resized and/or reoriented to suit the area to be covered. It does however require a basic understanding of PhotoShop Layers.

In this exercise, let’s
assume we wish to cover over an
unsightly
object such as the alarm box pictured on this building.
It’s necessary to select a section of brickwork and to place
it
over the top of the alarm box in order to obliterate it.
This is the relevant section of the original image with the
corresponding display in the Layers Panel.
Use a suitable selection tool to
select an area of brickwork which
reasonably matches the area around the alarm box. In this
case,
the Rectangular Marquee tool was used, but you can use others if the
shape is not regular. 2-5 pixels of Feathering will help to
match
the new position.

Now hold down the Ctrl key and
press J. The marquee will
disappear and a new layer will appear on the Layers Panel, Layer 1.
This layer holds a copy of the selected area and initially it is sitting precisely on top of the original. You can also see that the name of the new layer, Layer 1, has a blue background, which signifies that it is the active layer and that whatever you do will apply to it. (You can change which layer is ‘active’ by clicking its name in the Layers Panel.)
With the Move Tool you can now
grab anywhere in your image and slide
Layer 1 about over the top of the background. In this way you
can
cover the box with the section of bricks. If the selection
doesn’t quite match in size because it’s from a
different
perspective, hold down Ctrl and press T. This takes you into
Free
Transform, which enables you to adjust the size, shape and
orientation.
Press Return when you’ve finished.