My central heat will not start,, just makes a clicking sound. I can turn the fan on but when I turn the heat on it clicks then the fan turns off... it is a gas unit... please help it is cold!

It could be a clogged pilot orifice or a dirty flame sensor.
There are also many other possibilities.
Check in the beginning of this board for the sticky notes they will help you figure out what is wrong.

Is this a doit yourselfer or do I need a pro?

First weather you need a pro or not depends upon how cold it is where you live.
It is a possibility that you could check something's out but you need some mechanical skills and the proper meter and tools.

I directed you to the sticky notes because if you can follow the material there it will almost walk you through some diagnostic procedures.

If you have no idea what the sticky notes talk about then you need to call a pro.

In other words there is no magic wands here or a special switch to turn on that makes fixing the furnace real easy. What we offer here is to try and answer intelligent questions posted by people who could use some help trying to figure out what is wrong with there equipment.

The first items I would check are what I posted above.
You can take the pilot out of the furnace and make sure the orifice is clean.
You can locate the flame sensor and clean it with some sand paper.
If you do not know where these items are the sticky notes have pictures that may be of help. If you need your heat right now then I would call a pro.