Since version Minecraft PE 0.16.0 the developers have added support for mods, so-called add-ons extension *.mcworld or *.mcpack which in turn can contain as the texture and modification.

To install Addons now you don't need to use BlockLauncher. Just run the file and it installed automatically. Then go to game settings and activate your addon

If you have downloaded a mod that has the extension *.zip or .*rar you will have to install the addon manually. To begin extract the contents of the files and see which folders are inside. There is directly the folder of the addon you will need to move in /games/com.mojang/behavior_packs but also there may be additionally a folder with the textures that you must move in /games/com.mojang/resource_packs

folder Structure MCPE:

• /games/com.mojang/behavior_packs – used for add-ons
• /games/com.mojang/minecraftpe – don't touch the contents of this folder
• /games/com.mojang/minecraftWorlds – used to install card
• /games/com.mojang/resource_packs – used to set textures (and sometimes for installing Addons)

If you have downloaded a mod that has the extension *.js or *.modpkg read the how to install scripts in Minecraft PE

P. S. If you want to view or change the contents of the file *.mcworld or *.mcpack then change the extension to *.zip and open the file in the usual archiver

For those who do not understand, I advise you to watch a video overview of the installation of the Addons