GRE Programming
I also just got a GRE PSR-500; I got it a little less than a month ago. My old scanner was a RS PRO-76, so this new one was/is my introduction to digital scanning, trunked scanning, access tones/codes, and all that modern stuff.
First, please do read the Easier to Read PRO-106/97/PSR500/600 Digital Scanner Manual for which Ensnared provided a link above. It is a huge help.
Also, since the GRE PSR-500 does not come with a printed manual, you might be happy to know that the Easier to Read Manual is available as a printed book. One place where you can get a copy ($29.95) is at Universal Radio in Reynoldsburg, OH:
Scanner Manual for GRE PSR500, Realistic Pro-106 and Realistic Pro-197.
Universal Radio is a good company, but I should warn you that they are currently out-of-stock on the books. I ordered one in December, and it was on backorder until Dec. 31st. I called this past Monday, the 14th, and they still don't have the books. (The ARC500 software on CD is also out-of-stock and on backorder.)
Second, regular analog frequencies are programmed into this scanner the same way as they are in old scanners, like the PRO-76. Just key in the frequency number, assign it to a "Scan List" (the new name for a Bank), and hit "Enter." Unlike the old PRO-76, however, you can give the frequency a name like "City Police" or "Sheriff" so you don't have to remember who uses which frequency.
Third, if you don't know anything about programming trunked channels, I recommend downloading a trial version of ARC500, PSREdit, or Win500 so you can see which one you like best, and getting a 1-year premium subscription to RadioReference.com so you can download trunk system frequencies and talk groups. (I found the ARC500 was the easiest for me to understand, and it gave me a good mental image of how data is arranged in the scanner.)
You can, of course, program the scanner by hand as others have said, but for a complete newbie (like me), being able to see on a computer how the frequencies, talk groups, and control channels are arranged and related to one another can be a big help.
The only trunking system with which I have any real experience is the APCO Project 25 (or simply "P25") trunked system. West Virginia is using this system for its Statewide Interoperable Radio Network, so all of the police, fire, EMS, and other services are going over to it, although they still are using their traditional frequencies as well in many places.
Not everything you see marked as "P25" in the RadioReference.com database is a P25 trunked frequency.
If you see something marked as Mode "P25" and it has a frequency number with it, such as "154.0100," you enter it into the scanner like a traditional frequency, but for the mode setting you select "P25" instead of "AM" or "FM" or "NFM" (narrow-band FM). AM, FM, and NFM are traditional analog frequencies, and P25 is a digital frequency. All four of these are called "Conventional Objects." (You can also select "Auto" as the mode, and the scanner will figure out what kind of signal it is receiving.)
To set up a P25 trunked system, however, you need to set up a trunk system (TSYS) first.
To do this, you must enter at least one frequency known as a "control" frequency for the tower that is closest to your location (marked in red numbers in the RR database). You should also enter the tower's "alternate control" frequency (marked in blue numbers) so the scanner has an option in case the first frequency isn't working for some reason.
You do not need to enter any of the frequency numbers listed in the database in black numbers.
Once you have a TSYS set up with at least one frequency in it, you can put in one or more talk group numbers (TGIDs), and then associate them with the TSYS you just set up. When the TGIDs are in and associated with a TSYS, you are ready to start scanning.
Please note that you are limited in the number of frequencies you can enter as a single TSYS in the scanner. The limit is 32 frequencies for a P25 system (other systems, such as LTR systems, have different limits). If you are entering both control frequencies and alternate control frequencies, that means you can put 16 towers' worth of frequencies into one TSYS. If you have more than 16 towers (32 frequencies), you need to create another TSYS.
Also, you can associate each talk group with only one TSYS. This is a bit of a pain for people like me who live in an area where the system you want to monitor is huge - state-wide - and you want to travel with your scanner.
I worked my way around this limitation by using the RR database to locate all of the towers with the widest range located along West Virginia's major roads, and programming them as a "Roads" TSYS. Then I associated State Police, DOH, and other related talk groups with that TSYS. Then I found the towers for specific geographic locations, put those in as separate TSYSs, and associated the relevant talk groups with those.
I hope this information helps you. Learning how the trunking systems work and how to get them programmed properly is a bit difficult, but once you see how all of the pieces fit together, it gets much easier. Whatever you do, don't get frustrated and give up. Keep posting your questions, and the people here will be kind enough to try to help.