Guinea pigs should be fed a diet of fresh Meadow Hay. Hay should be 80% of their daily diet. As grazing animals they need to eat all day and enough should be provided to satisfy their needs. Fresh vegetables and good quality pellets (I personally recommend ones with Vitamin C, we use Topflite Super Premium Rabbit and Guinea Pig Nuggets) should make up the remaining 20% of the daily diet.
Fresh wet Grass that had not been sprayed with chemicals is one of the best green foods for guinea pigs. Clean water should be available at all times usually from a water bottle otherwise heavy water bowl. Veges, fruit and grass needs to be discarded if it has been sitting around for a few hours.
Guinea pigs are social companion animals that require daily interaction.
They communicate by making various sounds that have different meanings and "popcorn," or jump in the air, when happy.
Average lifespan is 4 - 7 years but is not unheard of they can live longer.
Chew on objects to maintain all their teeth, which grow continuously.
Guinea pigs need their nails clipped approximately every three months.
Guinea Pigs could start being sexually mature about the age of 2 months, so it is a good idea to separate male and female babies before then.
Breeding Guinea Pigs should start at 6 months old and be over 600g in body weight. Female Guinea Pigs should have her first litter before she is 1 year old for health reasons.
Happy Cavy has a food list that you could follow.
Independent Cavy Clubs has a good Cavy Care section to read.
Guinea Lynx is another good read.