What's a better term for stupid user?

"Inexperienced" might be the right word here as most products/experiences/interfaces/etc. build upon other products/experiences/interfaces/etc. and the users who use one could have an upper hand in using another.

1. What is a better word for stupid?
2. What's a polite word for stupid?

What is a better word for stupid?

Foolish implies a lack of common sense or good judgment or, sometimes, a weakness of mind: a foolish decision; The child seems foolish. Fatuous implies being not only foolish, dull, and vacant in mind, but complacent and highly self-satisfied as well: fatuous and self-important; fatuous answers.

What's a polite word for stupid?

A partial list includes the following: airhead, beefheaded, beetleheaded, blockhead, bonehead, bullhead, bubblehead, buffle-headed, butthead, chucklehead, deadhead, fathead, flathead, hammerhead, heavy-headed, idleheaded, ironhead, jolt-headed, jughead, knucklehead, loggerheaded, lunkhead, meathead, muddlehead, pinhead ...