Writing a word and it jumps and has me finishing

This is a very common problem to people who purchase a new laptop, or change from a desktop computer to a laptop. When typing, the cursor suddenly moves all over the place (but usually up) and you find yourself typing elsewhere in the document.

The secret is... the touchpad.

When typing on a standard keyboard, people usually rest their palms on the front portion of the keyboard, or on a special palmrest. Typing on a laptop is a slightly different experience - you have to keep the hands more apart, to avoid placing them on the touchpad.
But even if the hands are apart, you have to move them slightly while typing to comfortably reach the upper rows of keys. Depending on typing habits, the movements will be larger or smaller, but there is always some movement.

Now consider this. If you look at your hand from the side, you will notice, that the base of your thumb protrudes down the lowest. When moving the hands while typing, you very gently touch/stroke the touchpad with the base of your thumb - even if you don't feel it :)
Unfortunately the touchpad feels it, and acts as if you deliberately moved the cursor and placed it somewhere above the spot in the document you were actually typing in.

There are two remedies.

First, and one that has to be excercised anyway, is to try and keep the palms well above the surface of the touchpad. It takes some practice to change one's typing habits, but eventually you'll do it. It's just a matter of finding a palm placement that will be equally comfortable, but will also lower the possibility of involuntarily touching the touchpad.

Second is to go to your system's controls, find settings for the pointing device, and search for options regarding touchpad sensitivity.

There are multiple flavors of these settings, so it's not possible to give one standard recipe, but if you have an original touchpad driver installed (as oposed to using a standard mouse driver, which is enough for the system to recognize the touchpad), there should be a special settings screen for it, and among other options, a sensitivity setting.
Sometimes there's also an option (checkbox) designed specifically to fix this issue - usually it's called something like "eliminate problems with light touch" or sth to that effect.

Please try it, I guarantee that in 99% of the "sudden cursor movement" cases this is the actual cause :)

Good luck, and please don't forget to come back and rate the tip if helped :)