Every song you have learned up until now has been in 4/4 time. While the great majority of folk songs are in 4/4 time, probably about 10-15% are in 3/4 time (sometimes called waltz time).
Playing in 3/4 time is no more difficult than 4/4 time, but you need to change your way of thinking a little. Instead of counting each measure as 1 - 2 - 3 - 4, each measure in 3/4 time will be
counted as 1 - 2 - 3.
Since there are only 3 beats in 3/4 time the pattern for bass notes and strums must be modified, because now there is not enough time for two bass notes and two strums.
The following example shows an alternating bass pattern with strumming. Notice that generally only one bass note is played in each measure of 3/4 time. In the first measure
you play the root bass note on the count of 1, then in the second measure you play the alternating bass note at the count of 1.