inserting into min heap
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 $0$ in the array given below 
 means no key at that index.
  $$\fbox{4}\fbox{6} \fbox{8}  \fbox{7}\fbox{0}\fbox{0} \fbox{0} \fbox{0}$$

After inserting $2$.

$$\fbox{4}\fbox{6} \fbox{8} \fbox{7}\fbox{2}\fbox{0} \fbox{0} \fbox{0}$$

But you need to maintain the min heap property. So 

$$\fbox{4}\fbox{2} \fbox{8} \fbox{7}\fbox{6}\fbox{0} \fbox{0} \fbox{0}$$

Again $2$ is less than $8$. So

$$\fbox{2}\fbox{4} \fbox{8} \fbox{7}\fbox{6}\fbox{0} \fbox{0} \fbox{0}$$