。
There's a man at the gate who wants to see you.
Literal
Gate [gen-の] place [at-に] you [obj-に] want-to-meet [ている] man [subj-が] exists.
~たがる ('show signs of wanting to,' 'want to (said of third person)') is the third-person version of ~たい. The ~ている form gives ongoing state: 会いたがっている = 'is wanting to meet.' The rule: Japanese speakers use ~たい only for themselves, not to ascribe wants to others without softening.