How to reserve a post in PPP?

I read some where that we can actually reserved an opportunity in PPP. Just now I saw 2 available opps for me. I reserved one, then click on the 2nd one, write the 2nd opp, submit my post and clicked back the opportunities page. I cannot see the 1st opp that I reserved minutes ago. Why? I cannot reserve a post like that? How to reserve a post? HELP!