taught, taut

Taught or taught is the past tense ( yesterday, or some time ago ) of teach, meaning to instruct or give lessons--
The kindergarten teacher taught them their ABC's.
His big brother taught him to ride a two-wheeler.

Taut or taut ( rhymes with taught ) means pulled tight or strained, meaning a rope or cord, or a person's nerves or muscles--
Keep the tent cords taut, so the tent won't sag.
He must have spent a lot of time at the gym to keep his stomach so taut.

Now that you know that, you can say--
"He taught them to keep the lines taut, and to watch in case a fish should bite."

Note--"tauten" is an uncommon word meaning to tighten a cord or increase the tension on a rope or cord--
If you tauten that rope any more, it may break.