The first thing you have to do is open up all your images in photoshop by going to File > Open

The next thing you do is choose which image you want as your background image and click and drag it so that it is separate from all your other photos. I chose this image:

Then go to your other images and find a photo you want to layer on top and go to the mouse tool that looks like this:

Click and drag your image over the top of your background image. Your layers should now look like this:

The easiest thing to do when making your clone is to make your Opacity lighter so that you can see both images:

Move your image around until your new layer is in a suitable place.

Now go to Layer > Layer Mask > Reveal All:

Your layers should now look like this:

Click on the Paint brush and make sure that your colours are black and white like below:

You can change the size of your brush size by going to the top of the toolbar on photoshop

now colour around your person/object rubbing out all the excess background. Your layer will look like this. You should have a white mark where the person is.

If you erase to much and want to bring some back, switch your colours to white so that you can colour in the bits you need.