Currently I'm trying to learn tline() by simply drawing the map. However, I have no idea how the parameters work. Apparently, according to the pico 8 wiki, tline()'s 5th and 6th parameters are expressed in "fractional map tiles" but I don't get what that means...
Can someone give a brief explanation?

https://www.lexaloffle.com/dl/docs/pico-8_manual.html#TLINE

I think the manual phrases it a bit better. The map coordinates are in tiles, so a tile coordinate of (2, 2) would correspond to the pixel coordinate (16, 16) because 1 tile is 8 pixels. The fractional part is because the coordinate doesn't have to be an integer, e.g. (2.5, 2.5) would correspond to 2.5 x 8 = (20, 20) in pixels.