When i type shift + 3 i get " instead of @ what could be the problem

Hello, please try pressing the option (alt) button + 2 instead of shift + 2

What it is! In a 4-speed automatic, D or drive is 3rd gear, and 4th gear is overdrive. If you have a 3-speed automatic, D is still 3rd gear.

Be sure that your keyboard is configured properly. You should be able to check under the "Region and Language" area of control panel if you are in windows and select "Keyboards and Languages." Check that it is set as a US keyboard or that it's set to which keyboard type you are using.

This happens when you have the keyboard set to be a UK keyboard instead of a USA one.
To get an @ on a UK keyboard, press shift + ' (the key two spaces to the light of "L")
To configure your keyboard to be a USA keyboard, go to the cControl Panel in your Operating system that sets the "Regional Settings" and set the keyboard to be a USA keyboard instead of a UK keyboard.
If you tell the operating system you are using in the comments section, I can provide more detailed instruction.

try using the key instead of the shift key

The keyboard is set up wrongly or the laptop isn't one set up for your country.
If you get " when typing @ try typing SHIFT and 2 for the @ symbol.
You can change keyboard settings in Control Panel.

While typing on my Smith Corona KA13, suddenly different letters and characters would type instead of the ones I was typing. Like an "H" instead of an "R". An "S" instead of a "D"..... Any help please..

This sounds like a language setting, have you tried changing the language to UK english?

This is because it is set to US english keyboard layout rather than UK English layout.

Go to Start -> Control Panel -> Keyboard

and change the language settings...