I've never understood adding fractions 1/3 + 1/4 ?

Divide each fraction and then add it

Multiply those to fractions by a number that will make both of their denominator the same and then add the numerators and keep the denominator as it is.
(multiply 1/3 by 4 and multiply 1/4 by 3 you will get 4/12 and 3/12 then add the numerators only and you will get 7/12 which is your final answer)    

Depends on snitch kind