I will also add a little bit to Abby-san's answer. The words he wrote is for formal situations that you will use with people older than you, like your boss, teacher etc.
If you want to use it with close friends and family members you can also use the informal versions of those words. Here are the words=>
1.Are you okay? => だいじょうぶ? (change the intonation at the end to make it sound like a question.)
2. I am okay. => だいじょうぶ。 (the intonation for this word will be like a regular/plain reply.)
3. I am not okay. => だいじょうぶじゃない!
Hope my answers were also helpful. がんばれ!^_^