Guinea Pigs require quite a lot of care, they need brushing, and sometimes bathing, their claws need to be cut once every month or so, and their teeth need to be checked weekly. These things can be done at home. You can can get a grooming set like the one by Options in the picture:
On the link it has a Grooming set suitable for Guinea pigs, it also has instructions on the back on how to groom a guinea pig (I have this set).
They need to be bathed every 6 months if they have short fur such as an Agouti, Abyssinian, or another short furred Guinea Pig, Long coat Guinea pigs need a bath every 3-4 months. The time in-between baths varies, due to cage size, the sex etc... If the cage is quite small, a short coat would be every 5 months, and a long every 3 months. If they're male, every 3 months for long fur, and every 4 months for short fur. In the picture are my 2 Guinea Pigs just before a bath, sitting in the sink with towels. Here is a link (Not owned by me) on how to bath Guinea Pigs: