How long is navy sea tour?

Currently in DEP program to be a nuc and I was reading something that said our first sea tour is 48 months and first shore tour is 36 months. But if I am enlisted for 6 years and 2 of which is schooling will I ever get a shore duty or am I always at sea since 48 months is 4 years. How does sea/shore tours work? And what is a "sea" tour exactly, it it sitting at port in another country or is it sailing for 4 years lol?