Call and describe the tree: what it is, where it stands, what it is leaning over. The crew sets a time to come out, looks at it, and hands you a written estimate on the spot. There is no charge for the visit or the estimate.
If a phone call is inconvenient, send the form with the address and a line about the tree, and you get a call back the same day. For a tree on the house, call; the line takes messages at any hour.