A full body routine performed three days per week is probably the best way for a beginner to start weight training. However, this routine gets old fast. Within months or even weeks, you will outgrow it and you'll need to add exercises.
The problem is, the more exercises you add, the longer your workouts will become. If your workouts are too long, you begin to reach a point of diminishing returns, and ultimately, the excessive duration has a negative effect. The solution is a split routine. A split routine means that instead of doing all your exercises in one session, you "SPLIT" your body in half and train one half on DAY ONE and the second half on DAY TWO….
Adding more exercises allows you to:

1) Work each muscle more thoroughly and more deeply into the fibers
2) Work the entire muscle group; for example, front deltoid, side deltoid AND rear deltoid
3) Concentrate on each muscle more instead of spreading your attention out
4) Apply more energy and effort to each body part instead of holding back and conserving energy for the last few muscles

2 Day Workout Training Split Routines