through: preposition.

Examples:

I used a knife to cut through the watermelon.

I walked through the park at a leisurely pace.

throw: verb (action)

Example: Some major league pitchers throw the ball at speeds exceeding 90 miles per hour.

threw: verb; past tense of throw.

Example: I threw the ball to the first  baseman.

Through and threw are homophones, or words that sound the same but are spelled differently. Sale and sail, weigh and way are other pairs of homophones.