Pull-ups are one of the ultimate tests of relative strength - your ability to move your own body weight through space. They build wide, thick lats, strong biceps, and the kind of functional upper body strength that transfers to everything from climbing to carrying groceries. If you can't do one yet, the progressions below will get you there. If you can do ten, these same progressions will get you to twenty.
Start with dead hangs. Simply hanging from a bar for time builds grip strength and gets your shoulders and lats used to the demands of the movement. Progress to scapular pull-ups (pulling your shoulder blades down without bending your elbows) to activate the lats before the biceps take over. Next, use a resistance band looped around the bar and your knee to assist your first full pull-ups. Once you can do 3-5 band-assisted reps, transition to negative pull-ups: jump to the top position and slowly lower yourself over 3-5 seconds.
Once you can do 5 bodyweight pull-ups, focus on quality and volume. Do multiple sets throughout the day (grease the groove technique) rather than all reps in one session. As you approach 10 reps, add pauses at the top, slow the tempo on the way down, or begin adding weight with a dip belt. To get to 20 reps, you need to practice with submaximal sets (stopping 2-3 reps before failure) frequently throughout the week. Track your progress and be patient - consistent pull-up training over 3-6 months produces remarkable results.