First, you need to get y by itself on one side of the equal sign. To do that, start with any numbers without a variable: add six to both sides. Then move the x to the other side: subtract x from both sides. To separate y from the -4, divide both sides by -4 (remember that dividing a negative by a negative produces a positive). (REMEMBER: What you do to one side of the equal sign you must to do the other.)
Second, make sure your equation is in slope-intercept form: y=mx+b, where m is your slope and b is your y-intercept. Basically, put each section of the equation in order starting with the variable with the highest number of exponents. In this case, x (with an exponent of 1) will come first, followed by the 6 (with an exponent of 0).
One you have your equation in the correct order, you can determine the slope and y-intercept by matching it up with y=mx+b.