The way Free Gems for Clash Royale 2018 works is pretty simple: when you open the app, you'll see three sections you need to fill in with information. In the first, you need to enter your Clash Royale username to make sure you send the gems and coins to the right account; in the second, you enter how many gems you want; and in the third, you enter how many coins you want.
Once you've entered all this information (the numbers can be as high as you want), tap 'accept,' and a message will appear to confirm that the app is sending the gems and coins to your Clash Royale account. When this process is finished, you can go to your Clash Royale account and check if Free Gems for Clash Royale 2018 has made good on its promise.
Free Gems for Clash Royale 2018 is a relatively trustworthy app that promises to give you more coins and gems in Clash Royale.