一些英文句子解釋

1. 近排睇textbook, 見到以下句子:

e.g. Each student needs to be in the driver's seat.

成句點解? 咩叫做in the driver's seat?

2. 另外, 想問下All 既用法:

e.g. All students are/ is doing the assignment.

All 後面係用are or is?

Thanks.