The easiest way to think of it (for me, at least) is like a Gameboy. The Tama is the Gameboy (it has the screen and the buttons), and the figures are like game cartriges (they contain games and such that are separate from the Tama itself).
Not all the lite figures (the ones with a white base that come with your Tama) have the same game. Mine is a Mametchi (this guy
), and it has a game called "Cradles". When you plug them in, it says "Welcome!" and that's about it.
The full figures (the ones with the colored bases that are sold separately) each contain a few games and a shop/restaurant. Some of them also have an "Item" selection, for when the shops sell items. When you plug them in, not only does it say "Welcome!", but if you go to the clock screen you can see your Tama AND the Tama on the figure. Now, a weird and awesome little thing nobody tells you: If you happen to raise a Tama that you have as a figure, then when you plug that figure in, instead of buying things at the shop, you run it. For example, I somehow managed to raise a Mametchi (he's very hard to get) so now, when I plug in the Mametchi figure (the full one, not the lite one) I can run the Toy Store and get money that way.
I hope this was helpful!
Pikachi out.