What are bars and beats?
The beat is what you nod your head or tap your foot to when you hear a song you like. It is a pulse in music that everything lines up to. 99% of the time, a song will use a count of 4 beats, which we call a bar. Whatever strumming we do for 1 bar, we tend to repeat this throughout an entire song. So when you look at a song, only 1 bar of strumming may be shown, which you learn to repeat while playing whatever chord is written. How fast you count this 1, 2, 3, 4 is called the tempo, aka speed or bpm (beats per minute)
This is a great place to start when learning any new song as it gives you chance to learn the chord changes. Plus- many real songs actually start like this! Count 1, 2, 3, 4 at a slow, even pace (out loud if needs be) and strum an E chord every time you say beat 1.
The strumming for any song is only shown as a 1 bar pattern. This is generally repeated for an entire song.