Tortoises as pet:

Tortoises can make interesting pets, though they can present a challenge, due to their size and dietary habits. Their diets vary from species to species, but all need quite a variety of foods, with careful attention paid to the amount of roughage and calcium/phosphorus balance. Depending on the temperatures where the tortoise originates and the area where you live, it may be indispensable to bring the tortoises indoors overnight or during cooler weather.
Some species need to hibernate, which can be quite stressful for the tortoise and thus requires special conditions.
Tortoises don't interact with or particularly like humans. You must be prepared to have a pet that doesn't interact with you other than at feeding time.
They also require clean fresh water and bedding. You should be able to spend time each and every day cleaning and caring for your tortoise.
Tortoises possess very long life span(anywhere from 50 to over 100 years), which means you must be prepared to provide a lifetime of care and protection and also consider that your pet may even outlive you.
In a nutshell, if you are prepared to provide excellent nutrition, ample and adequate housing and a lifetime of caring to your pet, go ahead and get your tortoise! Pick a species that needs an environment similar to the one where you live and you can provide the best outdoor as well as indoor housing and nutrition.

Feeding:
Tortoises are exclusively herbivores. Their diets usually consist of plant origin. You can feed your tortoise vegetables like cabbage, lettuce, cauliflower, chopped carrots and fruits like cucumber, tomato, apple, pear and pineapple. However, fruit should be used sparingly because over consumption can lead to high levels of sugar in the intestine and result in colic.

Also remember to provide your pet with clean fresh water at all times.

Accommodation:
Tortoises live on land. Should a tortoise by accident fall into a pond or swimming pool it could sink to the bottom like a rock and drown. It is therefore very important when planning an enclosure for your tortoise that it has no access to large bodies of water other than a very shallow dish to drink from. when planning an outdoor enclosure you must make sure that you do not build it in an area of your yard which will flood during a heavy rainfall.

Care:
Soaking is a must affair for the proper care of your tortoise as it helps in keeping your tortoise hydrated, which in turn helps to keep the tortoise's system flushed. To correctly soak your tortoise, the water should be lukewarm and no deeper than the juncture between the bottom shell (plastron) and the top (carapace). Soak for at least five to ten minutes each time and make sure the tortoise is clean and dry when it goes back in its enclosure. Last but of course not the least, it is beneficial to remember that wild caught animals are much more difficult and expensive to care for than captive born.

Scientific classification of tortoises:

Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Testudines
Suborder: Cryptodira
Superfamily: Testudinoidea
Family: Testudinidae