A hybrid is a mix between different indica strains and different sativa strains. There are strains of hybrids that are indica dominate, sativa dominate or split 50/50. For example lets look at G-13 Diesel. This is a combination of G-13, which is an indica and Diesel, which is a sativa. This is a 50/50 hybrid so you will experience the effects of each. G-13 is good for anxiety, insomnia and relaxation. Diesel is good for anxiety, eye strain, headaches and muscle, joint and body pains. So when the two are mixed equally then the result will be a combination of both. Taste and smell will be effected as well, so Diesel has a more diesel odor and taste; where as G-13 is more sweet and fruity. So the end result will be a sweet and fruity diesel taste and smell.
If you pick a hybrid strain that is sativa dominate, then you feel the sativa effects more and if it is indica dominate the indica effects will dominate. So before you choose a hybrid strain you can look at what each strain does to determine what the hybrid will do for effect, taste and smell.