@oristarA,
Well, for starters, tack is a noun meaning how a ship sails in relation to the wind. Tack is also a noun which refers to the rope from the corner of a sail to the side of the ship away from the wind--the rope from the corner of the sail to the side of ship in the wind is the sheet. However, if you change from one tack (course in relation to the wind) to the opposite tack, the sheet becomes the tack (meaning rope) and the tack (meaning rope) becomes the sheet.
We're not done yet, though, not by a long chalk. Tack is also a verb, meaning to sail at an angle in relationship to the wind (and hence, the noun tack which refers to the ship's course). However, a sailing vessel cannot sail directly into the wind, so in order to go in the direction from which the wind is coming, it is necessary to tack--to sail at one angle to the wind, and then switch to the other. So, if the wind is from the north, you would sail northeast, and that would be the port or larboard tack (starboard, larboard and port--now there's some fun there), because the wind is coming over the larboard, or port, bow (meaning to the left, as you face forward from the rear of the ship--of course, if you are facing aft from the front of the ship, larboard, or port, is on your right). Then, you would sail to the northwest, on the starboard tack--meaning that the wind is coming over the starboard bow (which is to the right as you face forward from the rear of the ship--of course, if you are on the forecastle [pronounced foke-sul] or front of the ship, facing aft, starboard is on your left).
We've barely scratched the surface. To change from the port (or larboard) tack to the starboard tack, you can either tack (another verb meaning to cross the "eye" of the wind) changing course by about 100 degrees, with a high degree of difficulty for all but the best ships and crews; or, you can wear, a verb meaning to change course by turning away from the wind, and moving through an arc of about 250 degrees--much easier to accomplish, but extremely dangerous in battle, and a maneuver which will lose some of the distance you've gained, especially if your ship has a lot of leeway. So, to sail on those alternate courses is calling tacking.
Oh, i delight in the thought of introducing you to the language of sailing ships, because i know i can confuse you in a few paragraphs every time. The one thing tack does not mean to a blue-water sailor is this: