Generally, the only different between an eau de toilette (EDT) and a perfume (EDP) is the amount of actual perfume oil in the bottle. EDPs have a higher concentration and therefore will have a more intense scent and last longer.
HOWEVER, for some perfumes there is a significant difference between the actual fragrance depending on what concentration you choose. For example, Chanel No.19 is cold and green in EDT but warm and powdery in its EDP form. As a result, it's wise to sample both versions of a perfume before buying.
And eau de cologne (EDC) is even lighter than a EDT while an extrait is the most pure concentration.
All the best :)