Id Vs. Contractor

[mgurl 0]

hi.. I'm a newbie here and new at renovation concepts also.

I have a basic question and so sorry if it is a silly question

What's the difference between an ID and a contractor?

I suppose ID provides more design ideas and concepts?

Does it mean I cannot expect that from a contractor and that I'd have to specify the design to the contractor and he'll execute it?

How come sometimes I see quotations from contractors that are as expensive as an ID?

BTW, I did a search in the forum for a similar topic and didn't find one. If there is an existing thread on this, I'd be grateful if you point me in the right direction.