Bass note picking involves a single bass note followed by strumming a chord. Bass notes are generally regarded as being notes on the fourth, fifth and sixth strings.
In this turnaround, the bass notes are played on the first and fourth beats of each bar, and the written chord is strummed on the second and third beats. Even when the single bass note is played, the full chord is held in preparation for the strums to follow; e.g., in the first bar hold a C chord for all four counts.
In the following example a bass note is picked on the first and third beats. This "pickstrum" method of playing is very common in "country flavoured" songs. You will notice that the bass notes alternate between 2 strings for each chord.