First make sure you have downloaded and setup metamask for use with Polygon(Matic). If you need help with that, click here for a guide.
Open up Metamask by clicking the fox icon on your browser.
Make sure that you have some matic to send.
Press the send button.
Type in the address that you want to send to in the top box. It should start with
0x. Be sure to check it multiple times against the source since these transfers CAN'T be reversed.
Type in the amount that you want to send in the box that says amount. If you want to send all that you have, press the max button. Remember that you can't send every little MATIC that you have as you will need some to pay fees.
Press next once your amount is valid.
You'll see the total cost with fees to make the transfer. Review it all and once you are happy press confirm.
To see the progress of it, press activity on metamask. If it says pending it hasn't confirmed yet and should do so soon.
The top tranasaction will be the most recent one. Press it to see more details. Once you see transaction confirmed the transaction is fully sent. It can take some time is the network is busy.
Check out my other guides that might be helpful:
How To Download And Setup Metamask