If you see a link to a Yarrly on the internet while on your Android phone, it will be a link like this:
If you see that link in an email or on Facebook, Reddit or Twitter for example, simply tap the link on your phone. A window will pop up asking you if you want to open the link in your phone's web browser (like Chrome) or with Yarrly. Make sure you select Yarrly, and then the Yarrly will open in Yarrly. Once you have the Yarrly open, you can remix a Yarrly.
Tip: Once you select Yarrly as the app to open the link in, select 'Always' so your phone always uses Yarrly to open Yarrlys.