Carbon forms four covalent bonds by sharing its four valence electrons with four univalent atoms, e.g., hydrogen. After the formation of four bonds, carbon attains the electronic configuration of:

Carbon atom has 2 electrons in its innermost shell and 4 valence electrons. When it forms covalent bonds with 4 univalent atoms, it gets an additional 4 electrons as a result of sharing them. Now there are 8 electrons in its outermost shell. This resembles the electronic configuration of neon, which has the electronic configuration 2, 8.