Firstly there is no such thing as a bonsai tree, it is just Bonsai, Bon: being pot and sai: being tree. anyway, most of the Bonsai bought at garden centres and the like are from mass produced factory like places in Japan, the soil is sub standard and many of these trees will die very soon after getting them home, the trees will need to be watered a lot in the summer, as the shallow pot allows little soil and they dry out very quickly in warm weather, they are best watered by submersion to avoid washing away the soil and to ensure the water is getting through to the roots.
The right soil is a very essential element in Bonsai, go to a specialist Bonsai centre and look for a sail called Yakadama, not cheap but is the best. As for whether they are indoor or outdoor trees the best way to judge is by the type of tree you have, if it comes from a hot country . it will need to be indoors when its cold and outdoors in the sunny weather. remember Bonsai are just normal trees that are being stunted if you think you can keep a Bonsai without looking after it and finding information about keeping it pruned (that includes the roots) it will die. find out all about your bonsai on the net or buy a book and spend time looking after it and it will last for years.
Good luck