Antiretrovirals are medications that can only inhibit the replication of the virus. They cannot kill the virus in the way that antibiotics can with bacteria for example.
Antiretrovirals are divided into different classes (nucleotide analogue reverse transcriptase inhibitors, non-nucleotide analogue reverse transcriptase inhibitors, protease inhibitors and fusion inhibitors) according to the way in which they attack the virus. For example by blocking the virus so that it cannot enter the cell nucleus, by stopping new virus fragments from leaving the cell nucleus or completely obstructing the virus from penetrating a cell.
A good and clear explanation of all the currently available medications, the complex way they work and their side effects can be found on the Hiv Vereniging Nederland website.