Life Points
In RuneScape, your Life Points (LP) are a measure of how healthy your character is. Damage to your character reduces your Life Points. When they reach zero, your character dies. Lobster is a popular food because it restores a healthy 120 points per lobster and can be caught in bulk.
Catching Raw Lobsters
If you have a Fishing skill level of 40 or more you can catch raw lobsters at Cage/Harpoon fishing spots. You'll need a lobster pot. You'll gain 90 points of Fishing experience every time you successfully catch a lobster. Of course, the lobsters you catch while fishing are raw, and you'll need to cook them before you can eat them.
Cooking Raw Lobsters
You'll need a Cooking skill level of at least 40 to successfully cook lobsters. Until you reach 74 in Cooking, you stand a chance of accidentally burning lobsters while cooking, unless you have Cooking gauntlets. With Cooking gauntlets, you stop burning lobsters when your Cooking skill reaches 68. Each successfully cooked lobster gives you 120 points toward your Cooking skill.
Buying and Selling Lobsters
Because the price of a raw lobster is much higher than the price of a cooked lobster, it can be more cost-effective to sell your raw lobsters at the Grand Exchange and buy cooked ones. It can also be less time-consuming to have a local store convert your raw lobsters into banknotes for ease of transport, rather than carrying lobsters back and forth from fishing spots.