When I am typing sometimes the words move onto the wrong line or insert into other sentences I have already typed? An ideas why this is happening?
I don't think its the computers fault, I think it's yours.
I agree with Tina and Aibek that you are touching the touchpad with your wrist which is moving the cursor to another line. Some laptops of a touch pad disable hotkey. FN+ an F key. That should help stop the accidental presses.
Also check if your computer is vibrating due to some reason when you are typing. If it is, keep the laptop/desktop stable. Another common solution is to check if you have voice recognition software enabled, that often causes unintentional characters to appear.
what type of keyboard do you type on? Is it a laptop keyboard with a touchpad at its base? Or do you have a trackball on your keyboard?
To me it sounds like you're randomly hitting the touchpad or trackball with your fingers or palms and this makes the cursor jump to another position. You can turn off the touchpad to avoid this, here is the respective article: //www.makeuseof.com/tag/how-to-disable-the-touchpad-while-you-are-typing/
A similar question was asked previously: //www.makeuseof.com/answers/touchpad-cursor-jump-unexplained-areas-stop/
Just as Tina pointed out, it must be a touchpad. It frequently happens to me when using a keyboard on my laptop.