The Variables and Slow Transients Survey (VAST) on the Australian Square Kilometre Array Pathfinder (ASKAP) is designed to detect highly variable and transient radio sources on timescales from 5 s to 5 yr. We present the survey description, observation strategy and initial results from the VAST Phase I Pilot Survey. This pilot survey consists of ~162 h of observations conducted at a central frequency of 888 MHz between 2019 August and 2020 August, with a typical rms sensitivity of 0.24 mJy/beam, angular resolution of 12-20 arcseconds, and 5-13 repeats covering 5000 square degrees. An initial search of 1646 square degrees revealed 28 highly variable and/or transient sources, including known pulsars, flaring stars, active galactic nuclei, and sources with no multi-wavelength counterpart. Targeted searches including circular polarization of the Galactic Center and Magellanic Clouds further identified a Galactic Center Radio Transient and a very luminous pulsar. We discuss these findings and plans for a full 5-year survey which started in late 2022.