Sometimes a tortoise will need some time to feel comfortable before it begins to eat and drink.
Do be sure your tortoise has a proper home with a spot to hide out, a place to bask where the temperature is high enough, and tasty food and clean water available.
Give your tortoise time and space to adjust.
If you are really worried, you can always take your tortoise to a vet to be checked out. Sometimes new pets do carry diseases. A vet can tell you whether there is a serious problem.