Sure and certain are same. But if you add -ly (surely or certainly) it becomes adjective (kata sifat in bahasa). I'm sure that he is a boy. I'm certain that he is a boy. Both sentences show the same meanings. She certainly looks like a boy. She surely looks like a boy. Both certainly and surely are adjectives to show that her appearance is very similar to a boy. Have a nice day! ^^

"Sure" is a response like yes: "Sure I can help you". 'Certainly' means that you really will do something." Certainly, I will help you". More examples; She's certainly convinced that she's right - she's 100% convinced that she's right. Surely, you are impressed by her conviction - you must be impressed with her conviction, aren't you?

Most American native speakers say, "It SURE is warm today." According to grammar books, it should be "It SURELY is warm today." But everybody would say "It CERTAINLY is warm today." NOBODY would ever say "It certain is warm today."