Just go the place where your Barangay Chairman / Captain holds office. Usually, his / her assistant will give you a form to fill up. Attach an Id picture - usually 1 x 1 and pay the clearance fee.
In our barangay, its 50 pesos. There is no uniform fee structure for a barangay clearance.
The answer I gave is for a personal barangay clearance. If you want a barangay clearance for business purposes, the process may be different.
Have a nice day !