Well, currently I am using a game engine to develop a game. But, because that engine lacks decent multiplayer capabilities, I am developing a plugin for it to support multiplayer with Windows Sockets 2. At the moment, I do not know how to send variables (int, long, etc.) to clients, only strings. Is it even possible to send variables with WinSock

Multiplayer with Winsock
Rob McCaughey
Edwin Jeffcoat
Ajakati
You can send any chunk of data with WinSock - it doesn't know about strings or variables, it only knows about chunks of memory.
I must admit, though, that the fact you're asking this question suggests you need a much deeper understanding of the language than you currently have - particularly of topics like pointers - before you'll be able to get decent results out of WinSock.