If you are just starting out, then a little buzz is acceptable, in time as your technique improves, the buzz should disappear. Are you strumming really hard, does the buzzing diminish if you strum easier?
It may be your strumming too hard in which case you need to play less aggressively or have the action of the guitar checked by a luthier. Raising the action a little might help. Back to basics; confirm your fretting hand is in the correct position and that the fingers are contacting the strings at the right angle and just behind the fret.
Do not press too hard, sometimes pressing can cause uneven pressure on the strings. Have your guitars set up correctly; an experienced luthier will set up the action of the guitar to suit your playing style.
The truss rod will usually be adjusted as part of the setup. The guitars action and correct truss rod adjustment with the proper amount of relief can make an enormous difference to guitars playability.