For any element at index $i$ store its left chid at index $2i +1$ and right child at index $2i+2$.
Your heap in the form of array without any insertion. The $-1$$0$ in the array given below means no key at that index. $$\fbox{4}\fbox{6} \fbox{8} \fbox{7}\fbox{-1}\fbox{-1} \fbox{-1} \fbox{-1}$$$$\fbox{4}\fbox{6} \fbox{8} \fbox{7}\fbox{0}\fbox{0} \fbox{0} \fbox{0}$$
After inserting $2$.
$$\fbox{4}\fbox{6} \fbox{8} \fbox{7}\fbox{2}\fbox{-1} \fbox{-1} \fbox{-1}$$$$\fbox{4}\fbox{6} \fbox{8} \fbox{7}\fbox{2}\fbox{0} \fbox{0} \fbox{0}$$
But you need to maintain the min heap property. So
$$\fbox{4}\fbox{2} \fbox{8} \fbox{7}\fbox{6}\fbox{-1} \fbox{-1} \fbox{-1}$$$$\fbox{4}\fbox{2} \fbox{8} \fbox{7}\fbox{6}\fbox{0} \fbox{0} \fbox{0}$$
Again $2$ is less than $8$. So
$$\fbox{2}\fbox{4} \fbox{8} \fbox{7}\fbox{6}\fbox{-1} \fbox{-1} \fbox{-1}$$$$\fbox{2}\fbox{4} \fbox{8} \fbox{7}\fbox{6}\fbox{0} \fbox{0} \fbox{0}$$