If someone plays the harrowing does he target something and puts it on the chain? If so can I disposal order that card before it resolves?

Yes, you can use Disposal Order to prevent a unit from being played by The Harrowing.

Here is how the interaction works:

1. The Harrowing is played

• When your opponent plays The Harrowing, they must choose a unit in their trash as a target. Because the spell's instructions require choosing a specific game object (the unit in the trash), that unit is targeted when The Harrowing is added to the chain.
• The Harrowing is now a pending item on the chain, and the game state is Closed.

2. You react with Disposal Order

• Because Disposal Order has the Reaction keyword, you can play it while The Harrowing is still on the chain waiting to resolve.
• You play Disposal Order and choose the unit your opponent targeted with The Harrowing (and up to two other cards) from their trash.
• These cards are then recycled to the bottom of their owner's deck.

3. Resolution

• The chain resolves in reverse order (LIFO). Disposal Order resolves first, and those cards are moved to the deck.
• Next, The Harrowing attempts to resolve. Because the unit it was targeting is no longer in the trash (it has changed zones to the deck), the target is now illegal.
• Per Rule 359.3.e.1, the spell resolves anyway, but because its instruction cannot be executed (there is no valid unit to play), it has no effect on the board.

Summary: By reacting to The Harrowing with Disposal Order, you move the intended unit out of the trash before The Harrowing can pull it into play, effectively countering the spell's primary effect.