How do the 2 bytes that represent each tile correlate to where the tile is positioned and how do you know which two bytes represent which tile in the editor?
Imagine the picture of the title screen. Now slice it horizontally every 8 pixels. Do the same vertically. You will end up with a bunch of 8x8 pieces - thats the tiles. Then imagine you line up those tiles in a separate place and give each a numbers from 0 to N.
How you gonna recover the picture from these tiles? You need a map that tells you where to put each piece. Since SNES resolution is 256x224, imagine a table with 32 columns and 28 rows (32x28). In each cell there is a number - that number is a tile number (0 to N).
Thats essentially what Tile Map is - a 2d table with tile numbers in the cells (and some extra info as chillyfeez explained). Technically speaking Tile Map is 2d table represented linearly (1d), because memory is always 1d. That simply mean that you line-up first row, then second row,... That way of constructing is usually simplified as
"left to right, top to bottom"Example:
Lets take 99 08 from memory $46160$46160-$46000 = $160 = 352 (decimal)
352 / 2 = 176 (we divide by 2 because each cell is 2 bytes)
176 / 32 = 5 (32 because 1 row is 32 tiles)
176 mod 32 = 16
Then the tile with number $99 (153 decimal) is on 5th row, 16th column.
We have EVEN MORE themes now, but some old ones are gone...