Hello. Thanks for the feedback and thanks also for trying my game.
You can change key bindings from the menu. "Escape -> Options -> Bindings".
To start building with the default control scheme, use the mouse wheel to scroll through objects that can be built, then press B to begin building.
In addition to the "I" key, by default, the inventory screen will also open if you press the C key because it opens the crafting menu which is part of the inventory screen.
I will be around and more than happy to answer any questions that come up as you play the game. Thanks again.