What does 'just do it' mean? Please answer it in English

what does just do it mean? I just want to do what i want to do What does I'll just start early today!mean? I just loving you.what should i do?中文意思 What has he just done?And what does he want to do?的意思 I look beyond what I can not do,just focus on what I can do! Remember to do as what I said just now.He does not look like someone that fitness interests him very much.这两句话错在哪里? just do it 的广告词的含义?nike's ad just do it,what does it mean? i do not know what to do .为什么不用 what does ,what did what does Bob do? what does she do? What does tom do? what does friday do What does she do? what does Ann do i do not what you just stop by in my What __they__(do)when I called you just now? what i can do for you is just keeping you