1998 Nissan Sentra Car won't start, or starts sparingly.

My car is having problems starting. One mechanic stated that it might be the starter. I was under the impression that if the problem was the starter, the car wouldn't start at all.

I turn the ignition and
a) the car starts, or
b) the car produces a "clicking" sound.

I have replaced the terminals on the battery as an attempt at a cheap fix.

Help!