How do you insert a background for photoshop?

[Pika Power Haha]

Sry, i'm a bit new to photoshop and can't figure everything out.
Basically, i'm working on one of my pics which is a horse with a rider . And i finished the horse/rider part, but now i wanna work on the background which is basically blank at the moment. I found a pic which i'd like as the background, but i dont' know how to combine the two pictures without it looking transparent.. Sry if i'm not clear, but can anyone help? : )

[Brenton]

Ok first have both images open. The background and the horsepic. Do you have the horse and rider image trimmed out of its original background? If so good. If not you need to clip out the background on that one first. Then go back to the background that you want to place in. Go to Edit - select all or control - a. Then Edit - copy. Now go to the horse pic. Hit Edit - paste. This should automatically create a new layer for you. you can rearrange the layers by dragging one over the other. this way your background should be on the bottom. If you do not see the background after placing on the bottom layer then you did not clip out the horse background properly. IF you need to resize your background you can do edit -transform and it will change to a scale tool for you. Any help just holler.