You can make small corrections in existing text quite easily. Find a single character which is wrong or just pick any character. If the character is incorrect, you can replace it with the correct character by giving the command r c , where c is replaced by the correct character. Finally if the character which is incorrect should be replaced by more than one character, give the command s which substitutes a string of characters, ending with ESC, for it. If there are a small number of characters which are wrong you can precede s with a count of the number of characters to be replaced.
Counts are also useful with x to specify the number of characters to be deleted.
You already know almost enough to make changes at a higher level. All you need to know now is that the d key acts as a delete operator. Try the command dw to delete a word. Try hitting . Notice that this repeats the effect of the dw .