The map below shows the paths for unlocking guns and shooting ranges in the game. The first gun unlocked is the AK-47, and by the end of the tutorial you will also have access to the Colt 1911.
You may unlock any gun at any time through the Catalog, but it will cost less exp if you have found that gun on the map. Some guns will also require credits to unlock, as do shooting ranges if you do not have friends.
*The interactive map is not easily updated so you can find the updated pic on the guns page.*