What area of the country do you live in?
It might be too early to start up a pond and add
fish. Fish in water 55 degrees and lower aren't doing
much of anything except hanging around and snoozing
the winter away.

What you don't want to do is buy goldfish from the
pet store and move them outdoors if the temperature
from where they were living to your pond is too great a
drop. Which is why waiting until spring when you can
move the fish with about a ten degree difference in
temperatures.
Also can you estimate how many gallons your pond
is? That will give you an estimate on what your stocking
level should be. Rule of thumb is 20 to 40 gallons per
goldfish. Going with the higher figure is your best bet.
Too many fish in too little of water causes all sorts of
water quality problems. Keeping your stocking level
low is a good way to start learning and will help keep
your water from going green.
Which brings me to plants. Did the owners let you know
about the plants in the pond. More plants the better for
fish health all around. Do the plants in the pond need to be
cleaned up and trimmed up? A spring chore you can get
out of the way before adding fish.
Turning on the pump and getting the filter running before
adding fish should be your first task also (given you a lot
of first tasks here...) The filtering bio bugs won't get started
until the water temps stay above 40ish degrees.

If you are way up north, like I am, pond season is not even
in the picture. If you are in Florida, that's another story ;-)

kathy