The best way to get started with is to make sure you understand the fundamentals of boxing. Learning, drilling, and practicing these fundamentals in your first few weeks is essential to reap the full benefits of boxing training. The important concepts to understand are stance, movement, and striking.
Stance
Don’t underestimate the importance of correct posture and body positioning. In boxing this is referred to as your stance. Stance is a ready position from where you can execute punches, footwork and other techniques. A weak stance will undermine all your training so make sure to get this right.
⦿ Front toe & back heel on a center line. Dominant hand in back (if you are right-handed, put the right hand in back).
⦿ Weight evenly distributed across both legs, knees slightly bent.
⦿ Feet diagonal, a little wider than shoulder width apart, back heel raised.
⦿ Elbows down, hands up.
⦿ Head behind your hand/gloves, chin slightly down, eyes see over the gloves.
⦿ Relax and breathe!
Check out this guide from ExpertBoxing for further details on how to find and practice the correct boxing stance.
Movement
Once comfortable in your stance the next element of boxing fundamentals is movement. Focus on maintaining proper stance and angles while moving to box effectively. To do this, you will need to focus on developing footwork correctly. Beginners will typically jump around instead of using their stance and feet together. The basic step-drag is the best way of understanding how this works.
⦿ To go FORWARD or LEFT, step with your left foot first and then drag the right foot after.
⦿ To go BACKWARD or RIGHT, step with your right foot first and then drag the left foot after.
Following these rules will prevent you from walking or crossing your feet which may throw you off balance.
Striking
Start with the basics, get comfortable with the straight and hook punches (see the next section for details). This would be your jab, straight, and left/right hooks. Master each one individually then begin putting them together in 2 - 4 punch combinations. Throwing punches is simply the act of being relaxed, then quickly accelerating your hand towards the target as you exhale sharply. You tighten your fist on impact and then relax the hand to throw more punches. The trick is to utilize your entire body weight behind the punch without falling off balance. Skills and experience will teach you this over time.
For a beginner, the most important thing is to learn the proper punching form. Later on, you will be able to throw many different variations of punches from different positions and develop your own punching technique to fit your style.
ExpertBoxing has more details here.