i know the freg for the repeater has a _ offset and uses the 600khz
The negative 600KHz offset is the difference between the frequency you receive on and the frequency you transmit on. 600KHz is pretty standard on 2 meter VHF.
So, lets say you "hear" the repeater on 145.450MHz. To transmit into the repeater, you'd set your transmit frequency to 144.850MHz.
145.450MHz - 600KHz (0.6MHz) = 144.850MHz.
Some segments of the 2 meter band use a positive offset, + 600KHz, or the RX frequency + .600.
Don't confuse the 600kHz offset with the PL tone. The PL tone is a sub audible tone that is used to trigger the repeater. The repeater listens for this tone on the receiver, and only keys the transmitter if it hears that specific tone. This helps reduce interference from triggering the transmitter on the repeater.
PL (Motorola for "Private Line") is simply a CTCSS tone, or Continuous Tone Coded Squelch System. Kenwood uses the "QT" term, which stands for Quite Tone. They are all the same thing, generally, just different terminology. They are "sub audible" because they are (mostly) below the range of human hearing, so usually you won't hear them if you listen on a scanner. The repeater can "hear" these tones and will use them to trigger the transmitter.
While there are some amateur repeaters that still use carrier squelch, it is pretty rare. Most of the repeaters you will run in to will require a CTCSS tone to work. There is also a digital version, which uses a sub audible digital signal to do the same thing. These are called "DCS", digital coded squelch, DQT, Digital Quiet Tone, or DPL, Digital Private Line. They are usually expressed as a 3 digit number.
For what you are doing it sounds like, as others have said, that you need to set the correct tone on the transmit side. Without the correct tone set, you will not be able to bring up the repeater.
On the Kenwood software, you need to program your receive and transmit frequency. Then, click on the box for ENC QT/DQT. This is the "encode" tone setting. Encode just means it's putting it on the transmit side. When you click on that box, it'll give you a drop down menu where you can select the correct tone the repeater uses.
Do -NOT- set the DEC QT/DQT box. This is the "decode" tone setting, and if set incorrectly will prevent your radio for receiving.
So, what you need to do is either give us more information about the specific repeater so we can help you look it up and find the correct tone, or search for it yourself.
The tone itself will be listed in Hz, or Hertz, and will be somewhere between 67Hz and 254.1Hz.
Good luck!