Normally metal and non-metal form ionic bonds.
When Ca loses 2 electrons to stabilize it's valence shell it becomes a 2+ ion. When Cl gains 1 electron to stabilize it's valence shell it becomes a 1- ion. When two ions are involved in the formation of a compound, it is called an IONIC BOND.
Furthermore, during bond formation the electrons that are lost by Ca are transferred to Cl. When composing the formula for this compound, we need 1 Ca to supply the necessary electrons to satisfy 2 Cl.
The final formula is