You could start by downloading addons from the best, but currently most underrated addons spot on the planet
http://www.ofpec.com/addons/index.php All our addons are have TAG's so no conflicts are gonna happen...
you won't find any beta addons here either
and we test/review all our submissions to make sure they actually work..
and every addon has a version required section listed in its description.
Some other places will just upload any old thing and not tell ya anything about it
*The following was a paid advertisement by Kaliyuga and the OFPEC addons depot staff*
(Addon makers.. send in your submissions)
Once you've downloaded an addon you can just unzip it and place it either in your addons folder if it's an addon from CwC.. or your Res/Addons folder if it requires 1.85 and above
(earliest versions of OFP don't have an addons folder BTW)
as long as everything is working fine with the addon its self then you should have it available to you in the editor.