If you are training at home, a chin up bar is arguably the one essential piece of kit.

I use the Power Bar 2 from Amazon:

How to Do Your First Pull Ups

At your own risk – be careful – slow & controlled chin ups are essential to prevent injury

• Try putting a chair in front of you to place your feet on – this will make things a lot easier.
• Draw your belly inwards to activate your core
• Pull your shoulders blades together slightly to protect your shoulders
• Try and maintain a 3-1-3 tempo
  3 seconds pulling up, 1 second pause at the top, 3 seconds going down

DO NOT drop down as you extend your arms, you will forcefully hyperextend your elbows and stress your shoulders