Chemistry, covalent bonds. Please explain thoroughly. I know what a covalent bond is but this don't make sense.

Edit: It says an oxygen atoms has six electrons in its outermost energy level. Explain why two oxygen atoms must share four electrons when they form a covalent bond

Chemistry covalent bonds Please explain thoroughly I know what a covalent bond is but this dont make senseEdit It says an oxygen atoms has six electrons in its class=