Work permit

Dear Sirs,

I do have some questions regarding Immigration to Australia pls advise me the answers or let me know if there is any related links,

1-If somebody from Middle East get the job offer from an Australian company,he has to apply for Immigration or only as work permit?

2-If he has to choose Immigration how long it will take?

3-In this case can he bring his family at the time or he has to process after arrival in Australia?

4-If after a period,he wants to change his company what is the rule?
Can he change for example his State?

5-If I want to attend in Immigration Skilled worker in Australia,how can I assess myself that I am eligible or not?

6-If somebody choose an state for Skilled worker Immigration,can he change his state after a periode?

Looking forward to your replies,
With the best regards
Parham