Many users are using Meta trader 4 for forex trading, however i am confused as i have seen other trading platforms eg. Oanda which also has MT4. How are they linked? Which broker is good for MT4?

Meta trader just provides the interface (charts, indices, technical analysis indicators, etc). When a platform says they use MT4, it means that the platform uses the interface provided by meta trader. The platform on the other hand usually handles the cash flow and backend.

You can look at it like a bridge between the user and the platform. The user sees the platform and wants to get over there, but can’t cross over without the bridge. In the same context, the user wants to partake in online forex trading while the platform has the necessary code but no visuals, Meta Trader is the bridge that provide the visuals.