You wanna help the homeless kitties? GREAT!
First things first.
TNRM consists of 2 main parts: Sterilisation and management. Depending on your personal preference/lifestyle, you may want to do only sterilisation, but if you do management, then you MUST also sterilise (see how to sterilise stray cats?).
You can consider starting your own programme, or look for a group in your area and join them.
The important thing is to delineate an area you want to take charge of, and work within that area. It is also important to work with the authorities so your efforts are not wasted. (Ref: TNRM 101 – the Practical Handbook you can’t buy, but can read for FREE, and Tracking – TNRM Reimbursement from CWS)