Just go to your campaign list and click the pause button alongside the campaign you want to pause. Then just click again when you want to resume the campaign.
Be careful with your daily budget though, as Google works out your monthly spend by multiplying your daily budget by the number of days in the month. So if you stop your campaign for a few days you might find that Google increases your daily spend when the campaign is activated again in order to satisfy your monthly budget.
Posted in: Google Adwords