How does Gosu get the tiles on the screen?
While trying to write my own map class I use some code to assign every tile a pixel coordinate. Gosu then draws the tile where I want it.
But in Captain Ruby game, the Map class reads an array full of either ones or zeros and somehow knows where to put the tiles on the screen.
Here's where it creates the array the maps are in.

@tiles = Array.new(@width) do |x|
      Array.new(@height) do |y|
        case lines[y][x, 1]
        when '"'
          Tiles::Grass
        when '#'
          Tiles::Earth
        when 'x'
          @gems.push(CollectibleGem.new(gem_img, x * 50 + 25, y * 50 + 25))
          nil
        else
          nil
        end
      end
    end

Here we get the multi-dimensional array. It's full of 1's and 0's and nil. (I'm ignoring the gems for right now. Trying to keep things simple.)
This array becomes the raw material for the draw method:

def draw
    # Very primitive drawing function:
    # Draws all the tiles, some off-screen, some on-screen.
    @height.times do |y|
      @width.times do |x|
        tile = @tiles[x][y]
        if tile
          # Draw the tile with an offset (tile images have some overlap)
          # Scrolling is implemented here just as in the game objects.
          @tileset[tile].draw(x * 50 - 5, y * 50 - 5, 0)
        end
      end
    end
    @gems.each { |c| c.draw }
  end

This draw method is hard for me to understand. I don't know enough about ruby to decipher what's going on here.
What I do know:
I know the .times method. We do 'something' @height and @width times. Where height and width are the values taken from the map text file.
I get a little fuzzy when it creates the tile variable.
Then we get to the Gosu draw method.
The method parameters x * 50 -5 & y * 50 -5 decide where the tiles are drawn in the window.(I think.) But I don't understand what the x and y are and why you times them by 50. I mean, I know that x and y represent items in the @tiles array but... I'm confused :)
Any help to clarify would be appreciated.