Advice Wanted

I've got a question.
Where can I get information about tiles?

I don't understand how it works. Well I see that in 1 byte there are 2 pixels (4bpp), but how do tiles create? This is how I guess it works: we've got random palette with 16 colors, 1 byte corresponding to 2 pixels going in the row, 8x8 tiles (32 bytes in each) and each tile may contain 16 different colors max. And when I open ROM in Tile Layer or Tile Molester I can find tiles which containing looks of characters, so how is it happened? If these programs compare bytes with pixels from the beginning of ROM file there would be 1/32 chance that 8x8 tile will display correctly (bytes would be displaced), am I wrong?

OK, second. I thought tile consist of 32 bytes going in the row, and after one tile has been created only then we go to the next...smth like that =) But in The Molester there are buttons "Byte Forward" and "Byte Back" and when I click it I do not understand what's going on...so how is it work?

Thanks in advance