A photo of the area would be helpful. Is there and existing door there, window, etc.?
The framing of the opening of a door that size is fairly involved. You cannot just cut an opening and pop in a prehung door unit. Getting the doors to fit square, level and plumb so they operate properly can be a lot of work as well. You also have to consider if there are any electric, plumbing, vents, etc. in the are that would have to be relocated. Not completely out of the wheel house of an experienced DIYer, but don't make this your first big project without some guidance.
Kim, it's quite a bit of work! Also, just in case you need it, here are some instructional videos to help you.
More than you might surmise if it is to be weather proof and secure. Not to be taken lightly especially on an exterior door.
If dealing with no door in the wall you will also need a beam to support the wall/roof from caving in.