TN Visa for Candian in US ?

I have Canadian citizenship. If someone knows the TN Visa, please answer me several questions. Thanks.

The TN Visa is for Canadians to work in the US. Is it easy to get?

Some US employer asked me if I need sponsorship to work in the US. What does "sponsorship" mean? I thought that if I can get a job offer I can apply the TN Visa myself. Why sponsorship?

A lots of thanks.