How should i start my english autobiography?

Honestly, just start writing. You will no doubt need to re-write and revise often. You might even think of a good opening sentence after you finished your rough draft. You could use a flashback by telling something about you now ,then telling how you arrived to this point. Or think of some cute question to ask about the beginning of ones' life and then go on to tell the milestones of your life. Sometimes it feels awkward to write about yourself, but keep in mind that everyone has a life story. You are you and your story is just as important as the next one.