Pet doors allow your dog or cat to enter or leave your home without you having to open any door. There are many different styles. I have installed many of the plastic cat doors which fit in your screen door and allow your cat to go through the screen and come back inside without you having to slide the screen open.
As you can see from the video, some pets need doors even if theres no screen there at all. I guess it gives them a sense of security !
My own preference is for separate pet doors built into their own frame, or a brick wall or a wooden or steel door. At least that way they have a solid foundation and will be less likely to get damaged from constant use.
Its not always easy to put a hole in your house to mount a pet door so one compromise is to use a separate frame that you can put into a sliding patio door. The examples below show this application. While these items are more expensive, they do work and are built to last. They also have the advantage that when you move, you can take them with you, so long as your new house has a patio door.
Here is an example. These doors do take away some space from your patio door so if you have a small patio door it might not be suitable. You still need to able to open your patio door and have enough room to get out. You should also check to see if your patio door is compatible with this pet door. You still need to be able to lock the patio door and have it seal properly with the dog door installed.
Many pet doors are designed to installed on the bottom half of your sliding screen door. Here is an example of this style.
