My keyboard adds characters after I type certain letters or press keys? How can I rectify this?

For example, when I type an ' o ' , the cursor is then sent back to the beginning of the sentence. When I press the right hand 'arrow' key, it carries out the function then adds an ' i '. This happens with several keys.

This is happening on my MacBook 4.1 that I purchased as a second laptop to my pro, as I wanted something slightly retro and can take on adventures and not worry too much about damaging it!

ANY help appreciated!!