Question 564954
The elements of the functions are of the form (input, output).  So, find the ordered pair in f that has an input value of 2.  It's (2,1).  In other words, f(2)=1.  So g(f(2))=g(1).  Find the element of g that has an input value of 1.  It's (1,2), so g(1)=2.  Therefore, g(f(2))=2.
The domain of f is {2,4,5,-2} and the domain of g is {1,-2,5,6}, and the ranges of f and g are {2,4,5,-2} and {1,-2,5,6} respectively.  All the parts are similar, and knowing the domains and ranges of the functions should help you with understanding the composite functions.