Watch the video, or follow the steps. It's your choice!
Step 1: Get Minecraft, Dummy!
You were obviously going to need this but I thought I should mention it anyway. Go buy it, don't pirate it like a jerk.
Step 2: Get a Mod App and Block Launcher!
Step 3: Choose a Mod You Want
Scroll through the long list and find one that looks cool. Download it, it should open in Block Launcher if you use the suggested app.
Step 4: Enable Mod PE Script Support
Open Block Launcher, click the wrench at the top.
Click Launcher Options on the menu that comes up.
Scroll down to "Enable ModPE Script Support", enable it.
The launcher should restart.
Step 5: Enable Mods
Hit the wrench again once BlockLauncher restarts.
Tap "Manage ModPE Scripts"
Tap each mod and hit enable.
Step 6: Create a New World!
Create a new world. All your Mods should be installed! If you enjoyed this please favorite or subscribe to my YouTube channel here: http://adf.ly/1FnLRd.