I'm a little confused about the difference between this two sentences. Can you explain the exact meaning and all differences between this two?
Where did you sit last section?
Where were you sitting last section?
The exact difference is 100% in how the speaker is choosing to frame the event in time. There is no objective difference between them.
In the first, the speaker is choosing to treat the state of sitting as a single event; in the second, as an event extended in time.
The reasons for the speaker's choice cannot be answered without more context. Some examples of reasons they might have are:
If they are then going on to talk about something that happened during the section, they might choose the extended version (where were you sitting). If they are going on to talk about something that happened after the section, they might choose the punctual version (where did you sit).
They might see where were you sitting as more friendly and where did you sit as more formal or officious.
If the other person has just talked about how the room was very full when they entered, where did you sit is much more likely.