Okay, well, basically, the Y coordinate is the up/down axis, which you probably know. The x-coordinate is how far across the axis it goes. What
y = 2x - 3 means is that for every coordinate on the x axis we go across (1, 2, 3, 4), we will go up twice as many (on the up/down access) and we will come down three. That is where our coordinate will be.
For example, say x was equal to 2. Put a dot on the x axis where it says 2. Because x is 2, we need to go up 4 (twice 2) and down 3. So we'd be at 1. Therefore, you would put a dot where the 1 is on the y axis. Find where these dots meet, and that's your coordinate.
Not sure if you want anything a little more specific/different to this. Let me know if you don't understand.