Metals can be arranged in order of how reactive they are.

Metals high in the reactivity series can displace metals lower down.

Metals at the top of the series lose electrons easily and form positive ions.

Here are the main metals in the reactivity series starting with high reactivity:
K - Potassium
Na - Sodium
Ca - Calcium
Mg - Magnesium
Al - Aluminium
Fe - Iron
Pb - Lead
Cu - Copper
Hg - Mercury
Ag - Silver
Au - Gold