Instrumentar is passing the instruments to the surgeon. Like you see on TV when the doctor says "scalpel" and someone slaps it into his hand. In English, that is known as a "scrub nurse" (or "scrub tech" when referring to a technician instead of a nurse).

Circular is moving around the OR, outside of the surgical field, to bring in instruments from the sterile processing department and pass them to the scrub nurse. This is known as the "circulating nurse". The circulating nurse also sponges sweat (using forceps) from the brows of those in the sterile field, adjusts lights, and any other task that cannot be performed by those performing the operation.

SaludoZ!