Viruses are obligatory intracellular pathogens, meaning they can't proliferate without the help of a host cell's machinery and metabolism.
Although the replicative life cycle of viruses varies widely depending on the species and type of virus.
These are basic steps that all viruses must go through in order to replicate:
Adsorption: Anchoring of bacteriophage to the bacterial cell wall with the help of tails fibres.
Penetration: The phage DNA gets injected into bacteria.
Replication and synthesis: The bacterial DNA is disrupted and the viral genome takes charge of bacterial machinery. It starts making proteins required for replication and other structural proteins.
Assembly: Phage components are assembled into new viral particles.
Lysis and release: Bacterial cells are lysed and new viral particles are liberated to infect other cells.