Learning how to strum chords on guitar is probably the first goal of most people who take up learning the instrument.
For some it takes less than 4 weeks to accomplish this goal while for others it can take anywhere up to a year to achieve! It all depends to a lesser or greater extent upon your own individual aptitude for learning guitar and the quality of guitar lessons you learn from.
One of the first things you should know is that not all guitar lessons are created equally.
There are some really fine online lessons available but a lot more downright awful ones too.
When learning guitar and in this case, how to strum guitar chords, it's really important to begin by learning the easiest chords possible which are E minor and G Major.
They are not only the some of the easiest shapes to hold but also change between.
This is important since it gives you an immediate chord progression to practice your strumming patterns on.
The best way to proceed is to take 2 basic open chord shapes, such as the ones I've mentioned, and practice your strumming pattern on each one in turn.
The really difficultly comes when you try to connect them together.
You're going to find that there is a gap while your fingers make the transition from one chord to the next and that is what you want to get rid of! The aim is to make so that no noticeable gap exists as you change from one chord to the next as you strum...
it's easier said than done, believe me!