Step one: graduate from nursing school
(2ish-4 years, depending on what kind of program you attend -- get a BSN to be a more competitive candidate, because everyone and their brother wants to be a NICU nurse)
Step two: apply to nursing positions, including NICU. You may get a NICU position right out of school, you might not.
The beginning salary is entirely dependent upon what area of the country you live in.
Cons: The NICU is an ICU, especially a level 4. Babies die too. And sometimes, we take care of babies who should have been allowed to pass a long, long time ago, and we're keeping them alive despite their suffering. Don't just become a NICU nurse because you like babies. Shadow.
What is it that interests you about the NICU?