Cooking is one of the important skills in Runescape. The food you cook can heal you after combat. Remember the first few levels will be easy to gain. Once the levels get higher, it will take longer to get to the next level. Use all the opportunities to cook. Let's start real easy. There is a quest that can give you cooking experience at the Lumbridge Castle on the first floor. It's called Cook's Assistant.
Speak to the cook. After getting the ingredients the cook needs, you get a reward of 300 XP in cooking. That's the only quest that can give you cooking experience for non-members. Start by cooking shrimps and raw chickens. Net some shrimps.
Do this until your inventory is full of shrimps. Then take one shrimp and use it on a fire or range. (It is believed that the range in Lumbridge castle will burn less) Right click on the shrimp picture and click “all”. Then slowly all the shrimps will be cooked or burnt. As you get better at cooking, you will burn less. Then drop all burnt shrimps and sell all the cooked shrimps at a General Store. To get raw chicken, simply kill chickens, and when they die, pick up the raw chicken. There are chickens past the sheep fields in Lumbridge.
Once you get full inventory cook them all on a fire or range. Drop all burnt ones and sell all cooked ones. You can obtain beef by killing cows. (Not the cows that are black and white, cows that are brown and white) You can cook the raw beef from the cows. At level 10 you can make a Redberry pie. To make a pie: First get a pie dish. Then get grain and grind it into flour. Use the flour with a bucket/jug of water.
Use the water with the dough. Choose to make pastry dough when asked. Put the pastry dough into the pie dish. After that, add the filling you wish (red berries, meat, cooking apples) When that is done cook the incomplete pie on a range. You have a possibility of burning it. Then there you have it, your pie. At level 25 you can make stew. To make stew: Simply fill a bowl with water. Then get potatoes and put it in the bowl. Get meat (rat meat, beef…) and put it in the bowl as well. You have made an incomplete stew. Cook it on a range and then you have some stew. There is a possibility of spoiling the stew. Once your fishing is good enough, you can get fish and cook it. (You can get a lot of money by selling lots of cooked fish) Once you get up to level 32, you are allowed to enter the cooking guild, which is located near Varrock. You must be wearing a chef's hat to enter. There is no grain in the guild but there is a windmill to grind the grain. Bring some grain just in case.
Keep on cooking and have Fun!