Your language is nothing to apologize for. Many folks who have lived in English speaking lands their whole lives don't do as well.
The boss is a protrusion under the handwheel that your hand cranks is screwed into. There is a tongue and groove mounting that you really can't see on it unless you take the handcrank off.
The handcrank reverses the direction of the power in addition to spinning the head 3 revolutions per one crank. Nothing to worry about, but if other sewists use it, you will need to tell them.
I am not the best person to answer your presser foot answer. I love the machines, but sew very little.
I take my machines out and do demonstrations with them at folk life festivals.