I'm no expert - but you need to download the porting kit from paulthetall - you then download/create a 2k14 app file within that porting tool.
Read the instructions here - Once you wrap your head around it its not that hard - you do need to purchase 2k14 from the Steam App so you've got a licence key for it.
https://www.portingkit.com/aboutI purchased 2k14 from Steam so i watched this vid and worked it out.
In order i believe you download the porting kit / Download/create the 2k14 app file via the porting kit / then launch that - which takes you to Steam - you purchase the game and download it.
I did it ages ago but watch this vid below
https://www.youtube.com/watch?v=PEJU_F7lxskOnce done, you do launch to play or add mod files from finder on your mac - When you add mod files - you just right like on the app file and click 'show package files' then navigate through to the NBA2k14 folder (within the Steamapps folder i believe) then you drop all the files in.
For Roster files, again, right click and open package contents and navigate through the 'USER' folder and keep going until you find the 2k14 file - NOTE: You need to launch the game first for this folder to appear though, then exit and add the MOD roster files.
Good luck.