Explanation:
relative clause
it modifies noun phrase by some grammatical tools
for instance
my friend who just moved toAmerica is having dinner with us
here who is used to indicate the noun phrase
other tools like which that is also used
subject verb agreement
A subject and a verb must agree, even when other words or phrases come between them.
example
The flock of geese is flying south for the winter.
The subject is flock, so the verb should be is flying.
