Replace y by f(x), which BTW does NOT mean "f times x"
as you were taught earlier.  

f(x) = 7x - 11

"f(x)" means this:

If you substitute a number for x in "f(x)" and also for x in 
the right side of the equation that defines f(x) and simplify,
you will get the y-coordinate of the ordered pair that has 
that number as its x-coordinate which is a solution.

For instance

f(2) = 7(2) - 1
f(2) = 14 - 1
f(2) = 13

So the ordered pair (2,13) is a solution to

f(x) = 7x - 1

Edwin