Hi and welcome! Here are some tips:
Pellets: A good brand of pellets to get is Oxbow Cavy Cuisine for pigs 6 months and up, Oxbow Cavy Preformance for newborns to 6 months old (it has extra calcium for them to grow) and KMS Hayloft. You will need PLAIN Timothy pellets, no nuts, seeds, or colores bits. The amount of pellets to give your pig is 1/8 of a cup per pig, per day. Pigs under 6 months can have unlimited pellets.
Hay: Guinea pigs need a long grass hay to keep their teeth worn down and their gut moving. Good hay to give them is either Timothy or Orchard. There are more substitutes but I cant think of the other substitutes. Baby guinea pigs need Timothy hay, along with either parsley or alfalfa hay WITH their Timothy for extra calcium to grow. Alfalfa is not a long grass hay to be feeding your pig. Its a legume like a pea, and does not keep their teeth worn down. Guinea pigs need hay 24/7.
Water: People say water bottles are the best choice, because water dishes get too dirty and can flip over. If you are worried about extra minerals in the water and you have a Brita Filter you can use that (I use it)
Cage: A C&C cage is the best type of cage for a pig. If you look around you can see where to get DIY tips and items on how to build one. The minium space for two pigs is 2x4 grids. If you can fit it, 2x5 is preferred. Warning: if you get grids, make sure the squares are 9x9 in the grid. They changed some of them to 8x8 and peoplea guinea pigs were getting heads stuck in the bars.
Bedding: Nice beddings to use are either fleece, or kiln dried pine shavings/aspen shavings. Never use Cedar because the oils in it cause respitory and foot problems.
Hide Houses: Every guinea pig needs a hidey house. Dont get the medium size pigloo, those cause lack air circulation and who wants their pig sitting in a stink hut. Each hide house you get will need to have 1 entrance and 1 exit. Some people including me use RubberMaid stools for hidey houses. There are other house options besides stools dont worry.
Veggies: Good veggies to give your pig are: Green/red leaf lettuce, cherry tomato, carrots every once in awhile, and green bell peppers. Green bell peppers are a good source of vitamin c for a pig. Piggies cant make their own vitamin c, so giving them 1/8 of a green pepper a day will help them. To add about the carrots; guinea pigs cant process sugar that well, so keeping the amounts of fruit and carrots small and spread apart is best. There are other veggies you can give your pig and how often to, and what veggies are not good to give: (broken link removed)
Care and cleaning of your pig: Guinea pigs rarely need baths, unless they are super smelly or dirty. A good shampoo to use for your pig is either Gorgeous Guineas, or Squeaky Clean for small animals from a petstore. Also, their nails do grow and there are tutorials on how to clip them or have a vet clip them for you. If you ever need a vet, make sure they are an exotic pet vet and are cavy savy.
Getting a buddy and how to introduce: Guinea pigs are happier with a buddy. If you are looking to get a buddy, please check recues, craigslist, or petfinder. Do not go to a petstore or a breeder. This forum is anti-breeding/petstore and pro-adoption. Breeding guinea pigs is hard on the mother and babies. There are enough pigs without homes in the world, breeding makes it worse. Breeding also means a 20% chance the mom might die. Anyway back to buddies and introductions. You will need a same sex pig friend for your own pig, or if your pig is a girl you could also find a neutered boy. After you found your desired pig, there is a 21 day quarentine to make sure your new pig isnt sick. Quarentine needs to be in a different cage, in a different room. After quarentine is over, find a large open space for your pigs to meet. It needs to be on neutral ground where neither pig has been before. Do not just plop your guinea pigs in a cage, this needs to be done on neutral ground. Put a pile of some veggies in the area and a pile of hay, and put the pigs in the area. See this for more details:
https://www.cavyspirit.com/sociallife.htm
Thats all the (long) advice I have to offer
In my opinion, going to a petstore to "save a guinea pig" isnt really saving. Because then the store owners think they need more of a "stock" of guinea pigs and they order more. The mothers are bred back to back in a breeding mill, and kept in yucky conditions. Alot of the pigs are sick in petstores because of the conditions they're kept in. Breeding a sow means theres a 20% chance she may die. There are plenty of pigs in shelters homeless, why buy a pig from a petstore to have more be bred and fill his/her place?
