Onyour keyboard, look at the few keys in between the big block of alphabetic keys on the left andthe smaller block of numeric keys on the right. The bottom group of these 'extras' are the cursor control keys - now look at the top group. Unless yours is an unusual layout, the top left hand key of the group of six above the cursor keys should be marked something like 'ISRT', 'INSERT' or 'ISRT/DEL'. It is used to 'toggle' between 'insert' and 'overtype' modes. Each time you press it, it switches from one to the other. If your space bar is seeming to 'delete' characters, though what it is really doing is overtyping the character with a space, then press that key once and it should now insert a space by moving the other characters along one position.
Hope this helps.