You add them the same way you do with proper fractions. Make sure they have common denominators and add the numerators.
Example:
[tex] \frac{3}{2} + \frac{4}{3} [/tex]
[tex] \frac{3*3}{2*3} + \frac{4*2}{3*2} [/tex]
[tex] \frac{9}{6} + \frac{8}{6} [/tex]
[tex] \frac{9+8}{6} [/tex]
[tex] \frac{17}{6} [/tex]
