When you first open the PocketInvEditor you will be on the World selection. Choose the survival world to add items too.
After you select which world to add items too, you will come across the next screen which looks like this:
If you're wanting to start adding items, you should select "Edit Inventory" and that will pull up your current Minecraft PE inventory for the world you selected. Here is the inventory for the world I selected:
To add items to the inventory you need to get the menu to pop up. On my Galaxy S3 I use the menu button but it may be different depending on what phone you are using. When the menu pops up it will look like this:
You can add an empty slot which basically allows you to add an item you might not currently have. You will even be able to select stationary lava or water which thus far you are unable to have otherwise. From this menu you are also able to export or import the loadout, clear the entire inventory, and repair all of your armor and weapons that are getting low on durability.
If anyone needs any more guidance to using this app just let me know via comment or email.