The basic character of amine is due to the presence of lone pair of electron on nitrogen atom. Amines can easily donate this lone pair of electron on nitrogen atom to a suitable acid and form coordinate covalent bond.
CH3−NH2+HCl→CH3−NH+3+Cl−
In the above reaction, methylamine donates a pair of electrons to proton to form
methylammoniumion. Thus, it acts as a base.