A trolley is a small vehicle with wheels that can carry things. People can push trolleys.
There are different kind of trolleys. There are shopping trolleys which are used in supermarkets and other large stores with self-service. In American English these are called shopping carts. Customers can put things they want to buy in the trolley and then pay for everything at the checkout. Usually they are then allowed to wheel the trolley with the things they have bought out to their car.
Sometimes the customers have to pay a small deposit when collecting a trolley. The trolleys are chained together. The customer puts in a coin (in Britain a £1 coin) which he can have back again when he parks the trolley back in the trolley chain.
Trolleys are used in airports and some large railway stations for passengers to carry their luggage. Deposits are not refundable.
A trolley can also be a tea-trolley. This is a small trolley used traditionally in the house for plates, cups, saucers and sandwiches and cakes for afternoon tea. Tea-trolleys are also used in hospitals and offices to take cups of tea and coffee to people.
In American English "trolley" can be used to mean a tram (or streetcar). This is not to be confused with a trolleybus which is a bus which uses electricity from an overhead cable (like a tram).