For a start your starter motor is the cylindrical thing to the right of #9 in this picture
I'd check it has a good connection to ground (is the resistance between the - negative terminal of battery to the outer steel of the starter lots less than 1?)
Whip the seat off and check the starter relay and see if theres any corrosion and it's nice and tight. It's the translucent covered thing immediately up and to the left of the positive battery terminal.
What happens when you try and push start it? Do the pistons feel like they are pumping around when you let the clutch out? If they don't then maybe something has seized and the starter doesn't have the power to crank everything around so it just buzzes.
Lastly, it's probably not because if you have a green connector failure then I don't think any current would make it to the starter motor, but under the fuel tank there is a green connector that is famous for corroding and causing starting issues.