Having seen the error of his ways in going to the Thinkery and using its teachings to be dishonest, Strepsiades decides that the best course of action is to burn the place to the ground. As we discussed elsewhere (see "Symbolism, Imagery, Allegory"), there's a kind of parallel in this: Strepsiades is using literal fire to extinguish the kind of metaphorical "fire" that Socrates has started among Athenians with his immoral teachings (in the play, anyway).
It's not clear what's going to happen to Socrates and the other people in the Thinkery once the fire gets going, but Strepsiades is recommending that they, you know, flee the burning house. Seems reasonable—who said Strepsiades wasn't smart?