After download the application if you are a ios user go to setting > general > device management > click trust icon to verify the application.
I f you are a android user go to place where its downloaded...explorer > phone storage > download > tutuapp...Tap on it to open and will ask to install allow to it.
After downloading and installing TutuApp search Clash Royale there.It will appear now.Click on it to get.You will see clash Royale application downloading.
Tap on it to open the application and if you are a ios user you have to provide apple ID with password to continue the game with accepting some conditions & terms relating to the game.
If android user you have to provide your e-mail address with accepting some terms & service relating to tha game.
Now you can continue the game with using instructions provided by application.