When you first bring home your pet, make sure you have a safe place to put him/her when setting up your cage. (if not set up before hand: bedding, toys, shelter) make sure to place water and some food into your cage for your pet. Let him/her get used to his new environment and relax. Car rides home can be stressful on little animals. Then later, have some fun and play with your new pet. Get them used to human contact, by holding and petting. Always remember to feed and water.
When you first bring the guinea pig home and you already have another one at home, you need to keep them separate for a t least 2 weeks in case any of them has a disease. You will have to monitor the two until the sickness is healed. If you have no other guinea pig, the first day should be to let it know you and settle in the new home. For more information, visit http://jackiesguineapiggies.com/bringingaguineapighome.html.