What is first offer or LMO?

Hi,

according to information that I have, after I get an offer from a Canadian employer, the employer is required to apply to the Canadian government for permission to hire a foreigner. This is called the LMO (labor market opinion).

It sounds strange to me? Why this work in this order. It would me more logical to me if the employer first initiate LMO and get a permission form Canadian government to hire a foreigner and then, after such a permission is given, employer gives jobs offer to a foreigner.

Can anybody, plea, explain me the procedure?

Buy the way, I know that I can apply for the FSW immigration program if I have an job offer from a Canadian employer. Does it mean that I can apply before the LMO is done? Or LMO is a part of the consideration of my FSW application? Is it true that having an offer can choose between to options:
1. Initiate LMO and, in the case of positive result, enter Canada as temporal worker.
2. Apply for FSW immigration program, and in the case of positive result, immigrate to Canada.