I see some people have their pets friends with another one of their pets.How do you do that?

Go to the general 'Pets' page where it shows all of your pets. Next to each of your pets there will be an upside down triangle that you can click that will pull up a list. Click the 'Friends' option, and it will take you to the 'Pet Friends' page. There you can enter the name of the pet you want your pet to be friends with, along with the option to write a little description for them.

thanks