Aprovechar = to take advantage (situation), to make the most, to take the opportunity

Some example:
Aprovecha tu juventud= make the most of your youth;
Aprovecho la ocasión para decirles que …= I would like to take this opportunity to tell you that …

Aprovechar para/a (hacer algo) to do something

Aproveché para venir a verte= I thought I’d take the opportunity to come and see you;

Aprovecharse = to take advantage (person), to abuse
to exploit sth/sb
(abusar sexualmente) ~se de algn ‹de una mujer›
‹de un niño›
Se aprovechó de su ingenuidad para estafarle los ahorros.

Idiomatical use:

¡que aproveche!= enjoy your meal