What is covalent bond, and how is this bond useful for carbon?

The covalent bond is formed due to the sharing of electron between two atoms. If two-atom share one pair of the electron, the bond formed is a single bond .eg .H-H bond, Cl-Cl bond.If two-atom share two pair of the electron, the bond formed is a double bond.
For Eg O2 molecule, the double bond is formed between two Oxygen atoms.
Suppose two-atom share three pair of an electron, the bond formed is called a triple bond. For Eg in a Nitrogen molecule, two nitrogen atom share three pare of the electron.
The four atoms in the outermost orbit of carbon form a covalent bond with other atoms. Due to this, a wide variety of compounds are obtained. The branch of chemistry is called Organic Chemistry.

The bond formed by the sharing of the electron is called a covalent bond. configuration of is(k-2, L-4). In this configuration, we can see its valence electron is 4; therefore, it cannot lose or gain an electron to fulfil its octet. Then we say that Carbon is a tetravalent and covalent element. That's why carbon shares the electron with other elements to form a compound. 

A covalent bond is formed by the equal sharing of electrons from both the participating atoms. The atoms share electrons to form a bond to achieve stability in the outer shell, similar to the atoms of noble gases. Now carbon has four electrons in its outer shell. The carbon atom shares these electrons with other atoms and thus forms covalent bonds.

The covalent bond is formed between two or more non-metal metals due to the sharing of the electron.
Carbon needs four electrons to complete its octet. It is challenging to either lose or gain electrons, sharing electrons with the non-metals whose octet is incomplete. By doing so, carbon attains a very stable octet configuration.

A covalent bond is a chemical bond in which pairs of electrons are shared between two atoms. Carbon, having four electrons in its outer shell, has given it the ability to form innumerable molecules and bonds. It is why carbon has so many elements and allotropes.

When two atoms share an equal no. of electrons, a bond is a covalent bond. It is the strongest bond. As carbon is the tetravalent atom( has four valance electron in its outermost cell), it is hard for carbon to lose or gain all electrons. So, it shares its electron with other atoms to become stable, and it is possible by, as evident, a covalent bond.