Can you please explain what's a covalent bond and give some examples? would N-N be a covalent bond?

Ionic bonds are formed when an electron (or electrons) are actually transferred from one atom to another. Each (former) atom is made into an ion and the ionic attraction between + and - ions is the bond. However, bonds can also form by sharing electrons and these are called covalent bonds. Yes, :N:::N: is a covalent bond (technically three covalent bonds) as is H-H, Cl-Cl and all other diatomic species. But covalent bonds can form between different atoms also, such as CH4, CH3Cl, etc.