Assuming this is your scanner: RigPix Database - Bearcat/Uniden - BC-800XLT
Your 800 XLT was a very desirable scanner at one time as I believe the analog cellular frequencies were not blocked. (That feature is now useless as cell phones are now digital, also it is illegal to listen to cell phone calls (it was not illegal at the time this scanner was released as cell phones were few and far between and the law had not been written yet)
While it is 800Mhz it does not do trunking or digital (the new stuff a lot if not most areas are now using).
Here are the freq ranges: 29-54 / 118-135 / 136-174 / 406-512 / 800-912 MHz
You have 40 channels.
Note there are two antenna jacks in the rear. One is for VHF/UHF and one is for 800 MHz. Hopefully your scanner came with both.
It is very easy to program.
1) Press "Manual"
2) Press number "1"
3) Press "Manual" again
The scanner should now be on Channel 1
4) Simply enter the frequency you want to program, note the decimal point by the zero key.
5) Press the "E" button to enter the frequency into the scanner
6) Press "Manual" to advance to channel 2
7) Program the next channels the same way.
Press SCAN to start scanning!
Other info... The "DLY" button will add a 2 second delay to any channel. Press "Manual" to get to the channel you want to add a delay to and then press "DLY"
The "PRI" button in Priority, when pressed the scanner will check for traffic on channel 1 every few seconds regardless of what the scanner is doing (kind of a worthless feature in my opinion) if you notice the scanner "blipping" back to channel one or acting weird, it's probably because Priority has been turned on. The screen will display "PRI" when on, just press the button to turn it off.
The L/O button is "Lockout" you can lockout any channel that you do not want to scan or listen to. Say you only enter 10 frequencies you would want to lockout the others so the scanner skips them.
This scanner also has 2 "Banks", meaning the 40 channels are broke up into two sections of 20 channels each. Pressing the 20 button turns on and off the first bank pressing 40 turns on and off the second bank, unless you have frequencies programed past channel 20 you can ignore the 40 button. I believe by default Bank 2 (40 button) is off when the scanner is first turned on.
There is also a search function, but you will probably never use it. Just go to the Database here on RR and look up your area, hopefully you will find something that is not trunked or digital. (Technically you can listen to analog trunked with this scanner, I do it all the time with a non-trunking 800MHz scanner, but it can be a pain and might be confusing)
Hope that helps!