Why my pending claimed accounts is showing zero?
That is because you have not claimed any account yet and the moment you claim an account it will be updated as "1", similarly if you claim 2 accounts it will be updated as "2".
How much SP is required to claim an account?
Roughly 5000 SP is required, but do note that that it is the RC(Resource Credits) which is required to claim an account and as RC depends upon your SP, so roughly at 5000 SP you will have sufficient RCs to claim an account.
How does it work?
If you have sufficient RCs, then you can claim an account by simply clicking on the button "claim account" and after that the "pending claimed accounts" will be updated in your balance. So once you claim an account the number in "pending claimed accounts" will increase by one and your RCs will be reduced by some account.
You can find the "Claim Account" button in steemworld.org/@username. Just replace the username by your steem id.
The master keys and name of the account can be defined at a later stage if you want and you can claim as many accounts as you want, subject to the availability of RCs. So you claim number of accounts and can create it later on when you need those and any claimed account can be created as a steem account at any point of time and that is the beauty of this structure and resource credits.
Thank you and Have a great day.