A bond formed between two atoms by the overlap of singly occupied orbitals along their axes (end to end overlap) is called σ bond. Hence, 1s and 1s, 1s and $2p_x$ and 1s and 2s will form s bonds. π bonds are formed by the sidewise or lateral overlapping of p-orbitals. Hence, $p_y$ and $p_y$ orbitals will form p bond.