1. The first and last; signifies God's eternity: This idiom and its meaning, based on the first and last letters of the Greek alphabet, appears in the New Testament (Revelation 1:8): "I am Alpha and Omega, the beginning and the ending, saith the Lord," where it is repeated three more times.
2. The basic meaning of something; the crucial part; the most important aspect of something: Alpha and omega is the importance of the beginning and the end, the first and the last.

Sally had to master the alpha and omega of the new computer program before she could even begin.