Okay... You need to back up and take this one step at a time.
First, your main method is not an entry point. You need it to take a
String array as an argument.
Second, main is a static method, so you can't directly call instance (non-static) methods from it. In particular, you can't just call readgrades() or parsefile().
You should probably create an instance of gradecalc in main so you can call the methods on that.
Next, you have a method that creates a BufferedReader. But that's
all it does. There is no reference to a BufferedReader outside of that method, so the reader can't be used outside of that method. You might try declaring an instance variable to reference this.
Once you have a reference to the reader, you can use it to call readLine(). However, readLine() takes no arguments and it returns a String (not a double). Also, readLine() could throw an IOException, so you will probably want to put this call in a try/catch block.
Finally, parseDouble takes a String argument (not a double).