The first 3 Steem actually ends up in your account as Steem Power, which gives you just enough to start interacting with the Steem blockchain. You'll generally need a little more than this to really start posting and commenting, but it's sufficient that you won't be totally locked out (which can happen - if you have 0 SP then you won't even be able to initiate a transaction to "Power Up" your Steem)
The final, fourth Steem we take as a fee for our service.
But i have a question that whenever we creates a Account on Steemit then we automatically receive 15 steempower as a temporary Delegation from Steemit for enable us to do Comments and Posts, so in your service we get those 15 sbd Delegation or not at the starting ?
This is what @blocktrades was referring to in an earlier reply.
When we create an account we actually give you your 3 Steem back as Steem Power rather than as a delegation. This never expires, and you can build your account on this foundation.
With a free account you get a delegation, which has a finite life span, and although it gives you earlier access to more SP you will need to plan for it's expiration.
So, to directly answer your question, no: a purchased account through BlockTrades does not come with a delegation.