When you purchase shares in IPO they get credited in your Demat A/c Which is available online because now a days no physical share certificate is alloted to you.
So when they are not available in phyiscal form , you have the shares in online form i.e. in your demat a/c. By using these you can transfer these share to others a/c by way of sale and in case you purchase shares will be transfered to your dmat a/c automatically ...
I hope you will understand this..