Currently there is only one common way of installing mods is to install mods using the BlockLauncher. And let's just mention. Mods for BlockLauncher go only with the extension *.js or *.modpkg, so if you have downloaded the archive *.zip or *.rar you must first decompress and see what is inside. If the inside is *.js file will be folders with names like texture or behavior this addon and you need to read installation guide Addons

If your file has the extension *.mcworld or *.mcpack, also read the manual -> How to put Addons in MCPE

How to install mod with the extension *.js or *.modpkg in Minecraft Pocket Edition?

1. Install Block Launcher
   
2. Launch the game using Block Launcher
   
3. Click on the icon of a key appears next to MINECRAFT
   
4. In the popup menu, select ModPE Script or Import script
   
5. Press + and specify the path to our script. You can select a file from your device's memory, or to copy the URL of the js file from the download page fashion