Hello! Newbie here with questions !

Hello Everyone!!
My home was built in 1999 and I had the builder install home security wiring with sensors and also smoke detecters.
I want to install a home security system using what was installed and would like to do it myself.
The house has 24 4/C cables coming into my master BR closet.
At the backdoor coming in from the attached garage there is a blank cover receptacle and under it has a 4/C cable and not connected.
The 4/C Cables have a small (appears to be 22ga) BLACK/RED/YELLOW/GREEN conducters.
The windows and doors have a small, I guess proximity switch, imbedded in the window sills and also the door frames. However, I have not checked to see if they are connected to the wiring and also there is no magnet mounted or installed matching up to the sensor when the window or doors are closed.
The sensors are about 3/8"-1/2" in Diameter.
How can I test each cable and action with a multimeter and locate where each is coming from. I know this will take a while but none are marked with labels or tags.
Once this is done what system would be best to match up with what I have for control ? As I said earlier I would like to install as much as I can so I will be totally familiar with the system.
 
Lots of questions but if anyone can help get me started that would be great!

Being sort of new to all this stuff as a caveat, here is what I would do to start:
 
I would go to the endpoint with my multimeter and start checking all the pairs of one wire to see if they are all open or closed. Note down the result. Some may be closed if they were stapled/nailed through. You won't have a good picture until you're done cataloging.
 
Anyhoo then I would  wander out to the nearest door/window sensor with some blue tape and a magnet and tape the magnet to one of the switches. (If you are lucky perhaps the switches wiring is slightly visible and you can apply the multimeter right there.
 
Back I would wander to 'the other end' and start applying the old multimeter to see if anything had changed on any of the wire sets. Then I would note down the result.
 
this would be rather droll. It would be better if you had help, but probably only family would be willing to put up with this.
 
In my remodel I was able to completely hide some of the magnets inside the framing, so all one sees is the other part of the pair embedded in the door. But I have a hunch that this isn't the case in your setup.

I would be surprised if there are recessed contacts on the doors and windows, but no magnets.  The magnets would typically also be recessed, but might not be visible to you. 
 
I think the first step should be to identify all the cables.  You can do this with a multimeter, but it will be a slow process.  Using a cable tracker, like this one, will make the job easier.  You can find them at Home Depot and other big box stores as well.
 
With the cable tracker, you can connect the transmitter to a cable in your bedroom closet, and then go around to the doors and windows and find which one you pick up the signal on.
 
Once you have identified a cable to a particular door or window, you can connect a multimeter and get a resistance reading, then open the door or window and see if the reading changes.  If it does, that will tell you that there is an embedded magnet there already.  If it doesn't change, then try placing your own magnet near the contact and see if that does anything.
 
The blank cover plate you have near your entry from the garage is where you can mount a keypad for the alarm system.
 
There are lots of choices for which system to use.  One of the first questions you need to think about is whether you just want a basic alarm system, or whether you also want to use it as part of a home automation system.

That's a start for sure and I really appreciate the comments. Think I will invest in a cable tracker. I guess for now its best to mark and identify what I have now.
I cannot find any magnets at all on any door or window.
Does it matter what pr of wires or which colors constitute a "pair" in each cable. There is red,blk,yel,grn in each one ?
I'm quizzing my wife to see if the builder left any magnets or anything else along with all the pamphlets and warranty manuals on all the appliances and mechanical stuff in the house.

Got all doors, windows, and push button control receptacle with a blank cover on wall coming in to house from garage.Identified using small strong magnets. 2 doors I could not get to work and will replace the sensors and hopefully the wiring is good. Course they are in worse possible place to get to in attic. No magnets on any door or window. I tried a huge magnet on the 2 broke doors but still no action.
I have 4 fire detectors but no 4/c 22  going to them. Found 2 spare cables. So I still have 6 spares and it makes me wonder what the other 4 go too unless they are coiled in attic near the detectors.
I ended up with 18 inputs.
I would like to add the 2 doors and also a garage door sensor and also a main breaker panel on outside of house that to me is awful important and along with a driveway signal.
I'm gonna do the house layout on a drawing and number and tag all the cables to matchup.
Now its down to 2 repairs and then go forward.
So what system should I be looking into purchasing for just what I have and possibly the breaker panel and driveway alarms ?

It sounds like you have two issues.  Which cables are which, and are they wired to sensors.
 
The fastest way to sort out the wiring would be to use a signal tracer which includes a small tone generator which you could connect to the cable at the central panel, and then walk around the house with the tone detector and locate the door or window that cable is connected to.
 
Next, you could then put a ohm meter on the conductors of a cable and open and close the door or window that it runs to and check for a change in reading as the door or window is cycled.  You would also need to check the resistance readings to establish is the zone is both connected and does it use an "End Of Line" resistor and if so, what values.  The ELK supports either no EOL resistor(shorted loop) or a 2.2K EOL resistor configurations.

Finally got all wiring from sensors, repaired 2, bench wired panel and keypad, programed Vista 20 for 8 zones and am ready now to mount and terminate all wiring permanently to panel and activate system.
However I still need to hire a security watch company and decide how to have them watching without a home phone line. We are all cellular here and have been for some time. Is their a device to attach to the Vista and get service from security system. Also would like system to also dial my and my wifes phone on a zone alarm or a fault.
What are my choices ?