"Sheet" is the official term for the curling field of play. One end of the sheet looks like this:
| ========== | A
| ____ | 12 ft.
| / B \ |
| \__/ |
| | 21 ft.
| ... | (72 ft. of ice, then repeat)
A: The hack, the rubber block from which the skip pushes off when sliding. 12 feet back from the tee line (a line perpendicular to the sheet passing throught the button).
B: The house, the target for which the skip is aiming. (The small "o", theoretically in the center of the house, is the button, upon which a perfectly-aimed stone would land.)
C: The hog line. 21 feet from the tee line. The skip must release his stone before reaching this line.
Then there are 72 feet of ice, and the process is repeated in mirror image, resulting in a todal distance of 138 feet between hacks. Simple.