First select the Level in which you wish to play and click "Play with a Friend" button. Select your friend from the list of online friends and click the green "Send" button to send him/her a request. Your match will start immediately after your friend accepts your request.
Alternatively, you can send your friend an invitation via the "Send them invitation link". Simply copy and paste the link to any messenger and send it to the recipient. Your match will start immediately after your friend clicks on the link you have sent.
No "W" points or Trophies can be won in friendly matches. Please note that you can invite a friend and play for free in any level.