As for training, I rarely train my pets so you might want to rely on somebody better for that. As for feeding them, there should be a big blue tool-bar thing to your left when you're not on the forums... You should see the picture of your avatar's head, as well as one of your creatu. Either that or you can simply go to your profile.
Either way, click the link that says "SELECT" on the pet you want to feed. Then go to your inventory and click on a piece of food. It should have the option to feed to your creatu. If you don't have any food in your inventory, you might want to buy some. Then, after you're done feeding one pet and you want to feed the other one, simply hit the link "DESELECT" on the pet you've just selected, and "SELECT" another pet.
Your inventory is found by clicking the icon that is a picture of an apple. ;)
Most shops sell food, and you can buy certain foods in bulk. I notice that you want to try and buy foods that say can be fed to your pets with the effect of 15 hunger or higher. 10 isn't terrible, but if you have a dying or starving pet, it's better to get the 15 or higher deal.
Pizza, by the way, is more expensive than other food a lot of the time, but it can be fed to your pets usually with the effect of 30 hunger. Maybe 20. But its pretty up there.
The healthy food store has cheaper food choices usually. Keep an eye on the stores, by the way-- the prices change. Hope that helped. Rmail me if you have any more questions. ^_^