MArty2b - welcome to chordie. When trying to understand the timing of a song I find it is better to listen to the base notes to get the "beat" of the song. Strumming along with the song will help but you can also find the timing by tapping your fingers on a table your foot on the floor. There are many strum patterns that could be used and finding the right one will be "trial and error". (not as difficult as it sounds). As Roger said in his reply you can try 1,2,3, 1,2,3 for 3/4 timing or 1,2,3,4,1,2,3,4 for 4/4 timing. Keep in mind that when you are counting the "beats" of a song you will count all numbers as downstrums. This patterns would / could work for MANY songs but not all. If the song you are trying to play is a "blues" song the pattern could be a 1,&,2.&.3,&,4,&,1,&,2,&,3,&,4,&. With this pattern you would strum down on all the numbers and strum up for all the &'s. Other common patterns are 1,2,&,3,&4,&,1,2,&,3,&4,&...
Again there are many strum patterns out there and the same pattern can be used for slow songs, fast songs or anything in between. This is a process that you have to learn and understand for yourself but is as simple as practice. When you are listening to a song be it at home or while driving back and forth to school or work you can practice "strumming" to a song. Just give it some time and practice.
NELA