I don't think you can install/use the (ArmA2) tools unless you own ArmA2/OA
The only tools available now are ArmA2 tools, that just happen to mostly work with ArmA3
If you aren't buy/owning ArmA2, then you'll have to wait for the ArmA3 tool release.
At the moment 95% of ArmA2 mod'ing tutorials are valid for ArmA3 addons.