Typing is one of those skills that takes practice to learn. There’s never been an individual, the world’s fastest typists included, who sat down at a keyboard and immediately began typing.
The reason for this is the muscles in your hands and fingers need time to adjust to new movement patterns. That’s why it’s important to introduce a handful of keys at a time, and move on only once you’ve mastered them.
Depending on the program you use, you might start with the home row keys or focus on vowels and then consonants following a curriculum of English phonics. Some courses may have drills made up of nonsense letter combinations, and others, like Touch-type Read and Spell, might take a whole word approach, making the course easier to follow for people with learning differences.
The benefit of typing real words from the beginning is that once the movement patterns have been acquired, they are stored in muscle memory and become procedural knowledge. Procedural knowledge is something you know how to do automatically and don’t have to think about, like driving or riding a bike. Turning spelling into procedural knowledge can help individuals who have dyslexia because the letters and letter sequences are saved in memory as a pattern of key-strokes that the fingers type out automatically.