Correct spelling, explanation: the word personally is an adverb and if you want to form an adverb in English, you add -ly ending to an adjective. In the case of an adjective personal when you add the -ly ending you need to double -l letter as the last letter of an adjective is -l, too.

Definition of personally:
1. adverb – you use it when you want to present your opinion,
Personally, I don’t think you should do it.
2. adverb – done only by yourself,
I want to personally introduce all the changes to the project.

Expressions with personally:
1. to take something personally – it refers to some critical remark,
Don’t take it personally, but I think you should change your hairstyle.

Incorrect spelling, explanation: many users of English think that when creating an adverb from an adjective personal they don’t need to double the -l letter as it’s already there. However, in order to create the correct form, you need to double it. Therefore, the form personaly is wrong.