Why not looking matters
Every glance down breaks your place in the text and in your thinking. Readers of your emails and essays never see this, but you feel it as effort.
Touch typing removes that switching cost. The keyboard becomes something your hands know and your mind ignores.
Use the on-screen keyboard as scaffolding
An on-screen keyboard that highlights the next key is useful at the start, and a problem if it becomes permanent. Use it for the first lessons, then hide it and rely on the finger guide only.
When you get stuck, look at the screen rather than your hands. Your fingers learn faster when they have to find the key themselves.
Practice the common pairs
English repeats a small set of letter combinations: th, he, in, er, an, re, on and at. Typing these as single movements rather than two separate presses is most of what fluent typing is.
Practice them inside real words rather than as isolated pairs, so your hands learn the rhythm they will actually use. The same applies to word endings such as -ing, -tion and -ment, which appear constantly and quickly become automatic.
Expect a dip in speed during the first week of touch typing. You are trading a habit that works for one that works far better, and the trade is usually repaid within a few short sessions a day.