en_obs-tn/content/16/06.md

to tear down

This means, "to violently bring down" or, "to take down and destroy."

afraid of the people

Gideon was afraid that his fellow Israelites who worshiped the same idol would be angry with him.

waited until nighttime

Another way to say this would be, "waited until after dark." Gideon smashed the altar at night when everyone was asleep so that no one would see him do it.