Swing rhythm occurs when eighth notes are interpreted unevenly as a pattern of long-short durations (subdividing the quarter note into 3's).  Learn by practicing the count as:

Listen to the opening measures of G Minor Blues first played with straight eighths (counted: 1- &, 2- &, 3- &, 4- &) and then swing eighths (counted 1- &- a, 2- &- a, 3- &- a, 4- &- a):