Many people know this poem as "Gather Ye Rosebuds," and the saying "gather ye rosebuds while ye may" has become commonplace in our society. This saying can be loosely translated as "take advantage of today's opportunities." This poem is about how virgins should not wait but should get married, as it's better for them to find spouses while they are still attractive (and perhaps when they can still have children).
While this literal interpretation of Herrick's poem is a bit outdated according to cultural norms that put less pressure on women to marry and have children young, the poem can also be read as a reminder to take advantage of today. In other words, people should seize opportunities that are currently before them, and these opportunities are "rosebuds" that are fresh and available now but that might decay or not be around if people wait. Many of our opportunities are like freshly cut flowers, as they will not last forever. People reading and studying this poem today can see other applications of its message beyond marriage.