Can someone help me with the modding?

[Fka Blondie]

some of my mods arent working, they could be the mods. but my game doesnt show checkmarks like the game says it does. it just shows the letters b and t. idk wtf that means, i recently downloaded the game on my mac. the game is fantastic, but the modding is what im having a problem with. am i not putting them in the right folder? should they be in addons or workshop? as for the checkmark problem, could that be a glitch? if so what am i supposed to click. what does the mod mean when it is red? im lost.

[~Yak~]

Non-workshop addons (.vpk) extract from zip folder... and drag/drop to "addons" folder. As for MAC... can't help you there.

[Stark Raven]

If you are manually downloading, you want to place the .vpk file into the addons folder. The workshop folder will only clear out mods that don't match your subscription list. As a reminder, do not double-click the .vpk to install, that method is unreliable. Only drag and drop or copy/paste.

Regarding mod errors, it could be many things. The mod may not have a proper text description file, or it may be broken in some way. With regards to the Mac issue, I've heard some files with long names don't play well with the file system or something like that. If you have a mod with a long name, shorten the name to something you will remember before putting it in the addons folder.
(Note: I do not know the precise character limit or even if this still applies.)

Regarding the checkbox issue, that may be a problem with your game. Try verifying your game files from the Library.

Regarding mods listed in red, that is Left 4 Dead 2's conflict detection system. If two mods have the same type of file in them, the game will turn up a conflict and color those mods red in the list. Depending upon the nature of the conflict, most of these can be ignored. But if you have something like two Ellis mods active at the same time, then you should pay attention to the conflict.