Question

how to make sigma bond

Answer 1

In chemistry, sigma bonds (σ bonds) are the strongest type of covalent chemical bond.[1] They are formed by head-on overlapping between atomic orbitals. Sigma bonding is most simply defined for diatomic molecules using the language and tools of symmetry groups. In this formal approach, a σ-bond is symmetrical with respect to rotation about the bond axis. By this definition, common forms of sigma bonds are s+s, pz+pz, s+pz and dz2+dz2 (where z is defined as the axis of the bond or the internuclear axis).[2] Quantum theory also indicates that molecular orbitals (MO) of identical symmetry actually mix or hybridize. As a practical consequence of this mixing of diatomic molecules, the wavefunctions s+s and pz+pz molecular orbitals become blended. The extent of this mixing (or hybridization or blending) depends on the relative energies of the MO's of like symmetry.

Answer 2

Always the first formed bond is a Sigma bonds. They are strong bonds, formed by head on overlaping of Orbitals.
Ex- NaCl the bond betwn Na & Cl is sigma where as in. N2 or O2 First Formed is sigma & the others are pi. bonds.
One more thing b/w 2 atoms only one sigma bond exists -