how can I decompile a binary file using IDA? I tried opening it and it said it cannot find the entry point automatically and I don't know where to find it,
You mentioned that you want to analyze an ex5 file which is a MetaTrader5 file. That is not what IDA is for, that file is not an executable most likely. If the format isn't documented you can analyze the Application itself to figure out how it's made up, but most likely it's easier to just do it again.