Here, Michael Kuhn is at the helm with hand on the tiller. Karen, his wife, is on the active or leeward Jib Sheet. Which means that the taught rope (sheet) that is raising diagonal on the right hand side of the photo is holding the Jib Sail in its current trim. When Michael decides we are getting to close to the boats on the right hand side of this picture, he will declare "ready to tack". This is when we will shift the direction of the boat from 45 degree upwind port (diagonal left) to a 45 degree upwind starboard (diagonal right) direction upwind.
Karen will unfasten the jib sheet but still hold onto the sheet (rope) in front of her and respond "ready" and I will gather the windward or passive Jib Sheet in front of me and I declare "ready". Michael will then command "Helms Alee" which means he is turning the helm away from the wind (tiller or handle) to cause the boat to suddenly point to the right or starboard. As the boat is switching directions, the sails will stop come to the middle of the boat and then be caught by the wind on the opposite side. The forward momentum of the boat allows for the sail to luff (flutter in the wind) and then the sail fills with wind on the opposite side and suddenly flaps to its full position with wind. At the same time, I will then be holding the leeward or active jib sheet and then fasten it in the cleat (little black fasteners in front of me and Karen) after it catches the wind. The boat will now be traveling on a port tack (45 degrees upwind but on a diagonal right direction with the wind coming over the left-port side).
During this whole maneuver, Michael will switch sides of the boat to go to the new high side or where the wind is now coming from for visibility purposes.
If this orchestration of three people working together is not executed efficiently at the same time, then the time it takes to turn the boat from one tack to another takes longer and is possible that the boat will come to a stop while its waiting to catch wind from the opposite side into the sails.
What you don't see in all of these pictures is the JIB Sheet which is front of the person taking this photo.