How did Ottoman Empire start ?

The first ottoman sultan was Osman Gazi and

why did he make the ottoman empire,
how did this happen
and why ?
Update: i am sorry GUL V, but this is the wrong answer, plz check on your answer again, you will have to ba true turk to know this
Update 2: EVERY ANSWER HERE IS WRONG,
I am asking what made osman gazi make an empire and why
9 answers 9