Greetings, First of all your play needs to be Epic / Funny / Fail etc...
Then you will need to go to your match history, find the game and click on
Wait until the download finishes, and click on and the game will start.
Go to the time you made your play and click on "Record" button to start recording and again to stop.
Now the video has been recorded, go to "C:\Users\iFunzio\Documents\League of Legends\Highlights" You will find the video
And at "C:\Users\iFunzio\Documents\League of Legends\Replays" You will find the replay
Last step is that you upload your video to your YouTube channel and the replay on our website