What does it mean to use ports?

[hw]

Hi,

so I wanted to see what would happen if I used a port and removed the
emacs-nox packages and its dependencies.  Then I started installing the
emacs port.

What is going on here?  It seems as if I need to compile the whole
system myself now.

Is there a way to give all the answers to the questions about compile
options at the beginning?  I don't have time to sit around until the
next question shows up.

What if I want to change the compile options?  How do I make it so that
all the packages asking for me for options will do so again?  I don't
even remember all the packages that want to be compiled.

Can I globally set compile options like -march=native (or whatever the
equivalent for FreeBSD is)?