Please visit this page at the Terraria Community Forums for a detailed explanation on everything you need to do to get a multiplayer session of Terraria up and running!
https://forums.terraria.org/index.php?threads/terraria-mobile-1-3-multiplayer-setup-guide.82210/
The thread above is intended to be an overview/guide for setting up your very own multiplayer sessions for Mobile Terraria in the 1.3 era. As a reminder, you now have several options for hosting and playing multiplayer as compared to 1.2 era mobile, where it was limited to device-hosted local only. As a reminder, all of the following are now possible:
- Local Device-Hosted
- Local PC-Hosted
- Online Device-Hosted (Wifi Only)
- Online PC-Hosted
Multiplayer works across device families, so you should have no trouble connecting Android to iOS, Phones to Tablets, etc.
In general, Mobile Multiplayer now works like non-Steam PC multiplayer Terraria, so any guides or articles on that topic could also be useful if the guide below does not meet your needs.