You can focus on certain muscles each session, but I tend to feel that for beginners, 2-3 fullbody sessions per week is fairly appropriate, with 3 non-consecutive sessions per week being optimal for learning technique and making progress. Granted, specific goals will have some impact on the way you should train, but the main goal of a beginner should be, first and foremost, to learn how to do the basic compound movements with good form: squat, bench press, deadlift, overhead press, pull ups and rows (this may also include Olympic lifts if training for athletics or the sport of Weightlifting). The second goal should be to progress in one way or another (more weight, more reps or more sets) on every possible occasion. Note that sacrificing form to increase the weight or total reps completed is NOT progress -- you have only progressed if you are still performing the exercise correctly.
