If your pump is tied to an existing circuit that runs something else other than pool equipment, consult an electrician asap. Your pump/pool equipment should be on it own breaker and have weatherproof conduit protecting the electrical if it's outside. The cheapest option is as was mentioned to use the breaker to shut the motor on and off.
Besides that you have two choices, you can buy at Lowes, HD, Ace etc. a 220v rated switch which will look like a normal light switch. Get one rated for 20amps or so and "commercial duty", but look on your pump to be sure it's less than 20 amps in 220v mode. Buy a weatherproof single or preferably double gang box, weatherproof cover, 1/2" or 3/4" nipple, the corresponding lock ring and if your pool pump is hooked up already using a weatherproof cable and has enough wire you should be good to go.
The second choice is the intermatic timer, usually by the time you buy all of the above you're spending more or close to this:
Intermatic T104 208-277-Volt DPST 24 Hour Mechanical Time Switch - Intermatic Timer - Amazon.com It may be cheaper elsewhere as well.
If your pump is wired 120v all of the above still applies, you'll just buy slightly cheaper versions of a the switch or timer for 120v usage.
Guides to install and mount all of the above are online, but I'd recommend hiring an electrician if you are unfamiliar, especially since pool equipment needs to be bonded and grounded.
