First check the 'rag joint'.  In the engine compartment, it's a
flexible textile joint about halfway down the steering column.  There
should be only just a tiny bit of play at this point.  Replacing this
is cheap (parts <$20) and within the capabilities of almost any
backyard mechanic, as it requires no special tools nor skills.

Next look for leaks in the power steering actuator (looks like a
horizontal piston) or the hoses, as well as around the pump.  The
leaks will tell you what needs to be looked at next.  If it's dirty
it's hard to tell; clean it up and wait for the leaks to show.