This is a free app that manages mod files so that they can be loaded into Minecraft PE.  It is not possible to summon Herobrine without installing a mod. BlockLauncher only works with the paid version of Minecraft PE downloaded from the Google Play Store. Note that the mod described in this method does not currently work with version 0.10.0. One of the most popular sites is mcpedl.com. Because these are user created mods, there will likely be several to choose from, all with differing functions. One of the most highly-rated Herobrine mods on mcpedl.com is "Lord Herobrine". Another popular Herobrine mod is Herobrine/Holy Mod by mclover521. The instructions for installing both mods are the same. Find the download link to download the .js file to your Android device. Find the download link to download the .zip file to your Android device. You should see a "BlockLauncher" option on the main menu. Tap it to open the BlockLauncher menu. This will allow you to load the Herobrine Texture Pack.  Tap "Texture Pack". Tap "Select". Open the "Download" folder. Select the .zip file that you just downloaded. Select "Manage ModPE scripts". This will allow you to load the Herobrine script file.  Tap the "Import" button. Select "Local storage" from the list of options. Select your "Download" folder from the list of options. Tap the .js file that you downloaded. This will load the Herobrine mod into Minecraft PE. Now that you've loaded the Herobrine mod, you can summon Herobrine in your Minecraft game.  Gather your materials. You'll need two Gold Blocks, two Netherrack Blocks, and Flint and Steel. Stack the Gold Blocks on top of each other. Stack the Netherrack Blocks on top of the Gold Blocks to make a pillar. Use the Flint and Steel to start a Fire on top of the Netherrack. You will receive a message indicating that Herobrine has been summoned to your world.
Download and install the BlockLauncher app. Visit a Minecraft PE mod site. Search for a Herobrine mod. Tap the "Download Script" link at the bottom of the page. Tap the "Download Texture Pack" link. Start Minecraft PE. Select "Launcher Options (Requires restart)". Restart Minecraft PE and open the BlockLauncher menu again. Summon Herobrine.