You just have to click all of the +/subscribe buttons and Steam will download them for you. After you've launched Skyrim, wait for it to check the subscribed mods to make sure they're at their latest version (you'll only have to do this once unless you want them to always be updated) then click on Data Files or what ever it's called in the launcher and double check all of the mods are on then start the game. MAKE SURE YOU HAVE SKSE INSTALLED OR NOT ALL OF THE MODS WILL WORK. The version of the game shouldn't matter if you have Skyrim on Steam. Thing hasn't been updated in years