The chords placed above the lyrics are showing when the chord change is to be made- on those specific words in the song. If you're looking up a song that is unfamiliar to you, it would be virtually impossible to know how to play it with just the chords for the song. But if you look that song up on youtube say, and then play along with the song you'll be able to get the strumming/timing down. It's easiest to just strum to the beat. You can do all down strums until you're comfortable with the chord changes and then add 'up, down, ups' before each chord change and then just progress from there. Soon it will all 'click'