There is a big difference between how you hunt birds vs deer. For birds, you typically walk and flush the bird out, shooting them on the fly (or on the ground if you do not care about sport). A dog is helpful to help flush them out.

For deer, if you flush them out, generally it is a deer you have no hope of getting a decent shot.

For the beginner, bird hunting might be a better choice. You will get a lot of action right away, even if you do not come home with game. And as you bird hunt, you will encounter many deer, so you get a better grasp of where they bed down during day hours. Also, as you bird hunt, you can take note of deer trails. So your bird hunting this year can also serve as deer scouting for next year.

Deer hunting comes in two common forms: You can hunt from a stand at an area you expect to the deer to travel through or feed, and wait for them - archery works well for this as well as a gun. You can stalk (still hunt) a deer - this requires that you move at a snails pace (1 meter per minute or slower), keep quiet and make little movement - you have to be a lot quieter than when you bird hunt! Still hunting is the most challenging, but is perhaps the most rewarding - generally you still hunt with a gun, as it is difficult to get a good archery shot. Other ways to hunt are with a deer drive and also tracking - both of these require a LOT of land and a deer drive requires a group of hunters.

For deer hunting you need to hunt the wind and keep your sound, sight, and smell undetected by the deer.

If you go with a shotgun, get one with an additional interchangeable rifled barrel. Then you can use for both deer and birds.