in music when playing chords, you tend to have the strum pattern this can either be, d/u representing down or up or an upside down 'U' shape which represnts down. For example: The up beats are when the note is 'off' the beat
d u d d u
E E A7 A7 E
When trying to play a song that you have the chords to but not the rythem,the best thing to do is sing the song in your head as you play.By doing this you will be able to work the strumming pattern out quite easily.