everytime I try to trade between Pokémon from my white version to my black version it won’t let me is it because I’m not connected to the WiFi or I haven’t beat the game yet?
You can't connect to WiFi anymore because the Nintendo WFC (Nintendo Wifi Connection) has been shut down for DS and Wii games as of May 20, 2014. Unofficial servers have been created to replicate WiFi connection though, if you want to look for alternatives.
Hope this helped!
Source
Well, it can’t be that you haven’t completed the game, so I’m going to guess it’s just a WiFi thing. It doesn’t matter what point in the game you are, but it is required to have WiFi connection.
To get the C-Gear, you need to beat the Striaton City gym, then receive the C-Gear after helping Fennel.
Hope this helps! :)