Just a safety warning first: be sure to disconnect your battery wires first
before you disconnect and clean anything!! Since you are new at this, it
might be a good idea to wear safety glasses in case you accidentally short
something: The voltage being only 12 to 14V, it will not shock you, but will
cause sparks to fly that could throw bit of metal in your eyes.

I am assuming you don't have a "vehicle disable" alarm system. I am also
assuming your brother knows how to check for voltage across described
points.

Try starting the car by putting it in neutral if it is an automatic car. If
it starts, the switch inside the shifter is bad.

Make sure that all your fuses and fuseable links are ok. I don't have the
specific schematic to your year, but one fuse is usually labled "IG", "IGN"
or something similar -- make sure that one is indeed ok.

Put a voltmeter across the battery terminals. It should read 12 to14 volts.
Try and start the car - the voltage may drop, but it should drop much lower
than about 10V or so. If the voltage drops more than that, try starting the
car with booster cables. If it starts, your battery can't deliver the
current to start your car - replace it and see if that fixed it.

Get a piece of wood (a short length of 2x4) and a hammer. Put one end of the
2x4 on the starter, try and start the car and whack the other end of the 2x4
with your hammer. No need to break the starter, so dont hit is hard enough
so the case bends. You just want to mechanically shock it while you start
it. If it starts, chances are that your starter is bad. Even so, check
connections to the starter, etc. Most likely you will need a new starter.

Again, being very careful not to short anything, with a multimeter set to
measure at least 12VDC, measure across the fattest connection (usually a
thick wire, sometimes the thickness of a pinky) of the starter and to the
the engine body. You should see 12V here at all times, regardless whether
the key is in or not.
If you don't see this voltage, the fat lead does not make contact somewhere
between the battery and the starter -- it should be a direct connection, so
clean both sides - battery and starter end - and check it again. Before you
disconnect anything, disconnect the battery (see safety warning above).

Turn the key to the start position and keep it there, while your brother
measures the following:
On the starter, measure the voltage from the other (less thick, most likely)
contact to the engine body. When the key is turned to start, you should see
12V here. If you see 12V here and the car does not start, you starter
(actually the relay on top of the starter) is bad and the starter may need
to be replaced.
Before you toss the starter, disconnect the battery connections first and
clean the connections going to the starter by loosening the nuts on top of
the connections and cleaning them with some fine sandpaper.

If you don't see 12V, there are several things that can go wrong, depending
whether your car is automatic or stick. Report back with your findings.

Hope this will point you in the right direction.
Remco

Ahh, missed that.  Could be the contacts on the solenoid - on my Toyota they
need to be replaced occasionally.  Cheap and easy fix.
MZ