'Do you want a lift?' Lift here means a ride in a car (doesn't have to be a car but commonly is) to a destination. For example, "My friend gives me a lift to school" would be "My friend gives me a ride to school". I believe lift is far more common than ride, at least in the U.K. 'I'm being collected' This means that someone else is giving you a lift. Picked up can also be used instead of collected, and in my opinion is more common. Example: I gave my friend a lift to school and picked him up once it had finished. My friend usually gives me lifts to school and in return, my family will pick him up and drop him home.

''Do you want a lift?'= Do you want me to take you home in my car ? 'No thanks, I'm being collected.'' = No thank you, I am being picked up by car and taken home by someone else.

A lift means someone is offering you a ride in their car. Being collected means someone is coming to take you where you need to go. That's British English, though. In America English we say, "I'm being picked up." Hope this helps!