Lobsters are crustaceans, just like crabs and shrimps. This means that rather than having bones inside them, they grow strong shells to protect them. When ever they want to grow, crustaceans will have to produce a lot of mucus and slide out of their old shell, before growing a completely new one!
This will also mean puffing themselves up with water while they grow it, so they have room to grow inside the shell, and sometimes even eating their old shell to provide the calcium they need.
They feed on algae, seaweed and small animals such as shellfish. They have two claws, and they use them like a knife and fork with one huge claw used for crushing and one smaller claw used for slicing.
If a lobster loses a limb such as a claw or a leg which they sometimes do during fights, they can regrow it when they moult but it will take a while and will be very small for the next few moults.