That question is easier to ask then to answer!
Firstly, there are many different traditions in Buddhism, and all have their own variations on the practice. But even within one tradition, there are many different meditations one can practice.
Some practices are directed towards achieving better concentration, others towards developing wisdom and insight. Still other variations are analytical meditation, and meditations using visualization.
The aim is always to achieve control over the mind, so that we are not simply following every idea, thought or emotion that pops up in our mind, but we become more aware of what we are doing and why we do things. With that understanding and wisdom gradually arises.
If you really want to learn meditation, it is probably best to try and visit a Buddhist center or study group near you, and follow some meditation classes under the guidance of a qualified teacher or experienced student.