Hi, welcome to Armaholic and the game, I am sure you will have a great time playing it.
Since you discovered the addons and mods already you can be sure you have months of fun ahead of you constantly trying new content!
Since you have bought Reinforcements you will be able to enjoy all mods and addons for both Arma 2 and Arma 2: Operation Arrowhead. See these download sections:
- Arma 2 files
- Arma 2: OA files
** topic moved to the correct section, the Arma 3 section is only for Arma 3 (which is not even released yet).