Can we use "Person's name, When he verb to ..."

Can we say for example "Oussama, when he wants to do something he does it" rather than "When Oussama wants to do something he does it"?

What is the correct sentence grammatically, because someone said that the first sentence is bad expression to use because we mentioned the person's name alone without any verb?

Yes, it's perfectly permissible to put the subject's name at the beginning of the sentence in order to emphasise it. However, you don't need to include he, just another comma. The sentence is "Oussama does it" - the phrase "when he wants to do something," specifies when he does it.