If by 'Mod Manager' you mean the Nexus Mod Manager, that green button is supposed to start a download, and on completion if you have installed Nexus Mod Manager, the idea is Nexus Mod Manager would then install the mod ... It will not work for a lot of mods. TESNexus has enabled that button for just about everything on TESNexus and it is going to cause a lot of problems for people like yourself who have no idea about modding the game.
The files provided by Room207 for AMB will soon be dropped, instead he is now working on an OMOD (for use with OBMM) of the MaleBodyReplacerv5 (search for it on TESNexus). Currently there is a beta OMOD available but probably better waiting for the new version which will include the v5.2 files. Either which you intend to use you will still need to understand how to use OBMM. Nexus Mod Manager has a long way to go before it can handle scripted OMODS.
Roberts MaleBodyReplacerv5 files are manual install only. So you need to understand a fair bit about modding before even grabbing them. I have done a BAIN of the same files, but for that you need to understand how to use Wrye Bash properly.
I would suggest you start with either http://www.gamesas.com/index.php?/topic/449239-oblivion-mods-faq/ on this site (though it is a bit old now and has not been updated for ages) ...
Or better still - http://tescosi.com/wiki/Oblivion. A lot more up to date, Tomlong spent a lot of time over the last two years putting that site together with the best practices gathered from this forum and all the more experienced users.
Good luck - You have just opened a huge and complex hobby