Carbon has four valence electrons, so it can achieve a full outer energy level by forming four covalent bonds. When it bonds only with hydrogen, it forms compounds called hydrocarbons. Carbon can form single, double, or triple covalent bonds with other carbon atoms.
Due to having 4 valence electrons, carbon atoms must get 4 more in order to complete it's octet. Therefore, Carbon can make 4 covalent bonds in order to complete it's octet.
