How do you get a pet on rune scape

you have to do gertrudes cat quest
To begin the Quest, speak to Gertrude in her house west of Varrock and south of Juliet's House She will tell you that her Cat, Fluffs has ran away, but she can't leave the house to find her, as she is occupied with the job of looking after her Children. Accept the Quest and she will ask you to talk to her Sons, who might know the location of Fluffs.
You'll find Gertrude's Sons in the corner of Varrock center, near the Fur Seller and Benny, the Newspaper Seller. Talk to either of them and ask if they have seen Fluffs. They will tell you Fluffs has ran away to their 'secret hideout'. However, if you ask them where their hideout is, they won't tell you. They say they are short of cash, and will reveal the location of the hideout for 100gp. Once you give them 100gp, they will tell you the location of their Hideout - Varrock Lumber Mill. They will also tell you the only way into the hideout is by climbing over a broken fence on the southern side.
Now, head on over to the Lumber Mill. If you don't know where it is, follow the east path out of Varrock, and head north. After a short walk, you should find the Lumber Mill, but it is surrounded by a fence. By the Sawmill Operator's Hut is a broken fence, which you can climb over (no Agility level is required).You will then learn that the cat is thirsty, so use a bucket of milk with it. After feeding it some milk, try and pick it up again but it will still scratch you. You will then find out that it is hungry. So head back to Gertrude's house, and behind her house you should find some Doogle Leaves on the floor. Use the Doogle Leaves on a Raw Sardine, and you will get a Seasoned Sardine. Head back to the Lumber Mill, and use the Seasoned Sardine with Gertrude's Cat. Now try to pick it up, but it is afraid to leave, because it's Kitten is missing.
Now, head down the ladder and begin searching the crates. In one of the crates you will find Fluff's Kitten. The kitten is in one of the crates that in the top left corner of the screen, has 'Search' in yellow rather then the normal cyan color. After finding the kitten, head back up the ladder and use the kitten with Gertrude's cat. Both cats will then run off home. Return to Gertrude for your reward.
Congratulations! Quest Complete.
Rewards

• A Kitten!
• 1,525 Cooking experience.
• A Chocolate Cake and a Bowl of Stew.
• The ability to raise cats. See the cat care guide for more information.
• 1 Quest Point.

Cats
If your kitten/cat runs away, or becomes an Overgrown Cat, you can buy another kitten of Gertrude for the cheap price of 100gp. Be warned, when buying a new kitten you won't be able to choose what color it is. But if you wear the Ring of Charos(a) when purchasing a new kitten, you'll get the option to choose your color.If your kitten/cat manages to catch 100 mice, you can claim a special reward. Head to Gertrude, and tell her your cat has caught 100 mice. For a reward, she'll give you a special Cat Training Medal that can be worn in the necklace spot. It doesn't give any bonuses, or effects. It's mainly just for show. This is also a medium task in the varock achievement diary. The best places to catch mice are in Varrock Sewers and Evil Dave's Basement in Edgeville (must have started the evil Dave part of recipe for disaster)




hope this heleped