How do transition metals form ions?
How? By oxidation, which is formal loss of electrons.
Bulk metals are electron-rich species; their valence electrons are not localized to a particular centre, and these electrons are largely responsible for metallic properties: malleability; ductility; conduction of heat and electricity.
Since they are electron-rich species, metals are good reducing agents, electron donors. Given this the formation of positive metal ions, i.e.