You should also check for conflicts, if your mod manager warns you of a conflict then it's important that you see which mods are conflicting and disable the one you don't want to use. Bare in mind that if you do it manually you gotta be careful because if you mess it up there's little chance you can revert it (unless you make a backup), in which case you'll have to re-install - but the mod manager should save your mods.
The red mark is to do with something missing, if it says its something to do with the mod manager then uninstall the mod completely and do it manually, if you need help with putting things in the right places then there should be a readme either in the download or in the description, if not then there's a page somewhere on the nexus which tells you how to do it.
