Seat vs sit

I have an acquaintance here i CH, who speaks better English than I speak German. She has a problem with seat vs sit. So here's the explanation just for her:

Seat:
noun [C]
an item of furniture or part of a train, plane etc that has been designed for someone to sit on:

Sit:
1 [I or T; usually + adverb or preposition] to (cause someone to) be in a position in which the lower part of the body is resting on a seat or other type of support, with the upper part of the body vertical:

I have learned never to laugh about anybody who speaks a language bad. It only means that they speak another language better than you do. My tip is always to encourage people who try another language, not laugh about them trying. Except for when it's funny :)