You could get toomanyitems mod if you want it in survival or now in 1.8 you can go in creative mode.
Pressing 'E' will open your inventory.
Once you have installed Too Many Items, when you bring your inventory up, you can choose from a list of blocks/items that appears by the side and click them into your inventory.
You don't have an intrevory in minecraft, but we do have an inventory.
Press E
no
press e to access your inventory, then drag your items for the lower bar to your inventory
Tap the 3 dots next to where it shows your inventory.
Do you see the three white dots on the bottom of the screen? That is the inventory
Inv Edit basically allows you to spawn in items from your inventory.
On minecraft u have to mine it with a iron pick and if you mine it you should have it in your inventory
to keep inventory you can do /gamerule keepinventory true or /gamerule keepinventory false
do /clear inventory or just /clear