Some people manage to learn to type fast and accurately with little or no help, but most of us need some training to do it well. Even people who have grown up using a keyboard, and so type very fast, can do it much better if they take a course.
This is quite easy to do at home. In fact you can start by taking a test online. For most people, about 30 words a minute is fast enough - we only need to type as fast as we can think, and mostly our ideas don't really come much faster than that. Of course for a PA or in some other jobs, such as transcribing, you need to be much faster - speeds of 60 or 70 words a minute may be expected.
If you take a test and find your speed is below 30 words, it may be a good idea to improve your skills with an online typing course, or if it's important to become very proficient you can try a professional course such as Pitman.