The X-intercept is where the line on a graph hits the (X,0). The Y-intercept is where the line on the graph hits the points (0,Y).
Example: Y=2x+4 to find the Y intercept substitute a 0 in for X making the equation Y=2*0+4 or Y=4 meaning the Y-intercept is (0,4). For the X-intercept you have to substitute 0 in for the Y like this 0=2x+4 then you have to figure out what to multiply 2 by to cancel out the 4. in this case the x is 2, 0=2(2)+4 making the X-intercept (2,0).
To remember which is which just substitute 0 in for the one you aren't trying to find.