There are two main routes for a virus to enter a cell: endocytosis and fusion. Fusion only occurs in enveloped viruses, but endocytosis can occur in both naked (non-enveloped) and enveloped viruses. In fusion, the viral envelope and the host cell membrane fuse together, and the opening created allows the virus to enter the cell. In endocytosis, the virus is engulfed by the cell.
