Oh yeah, and how the heck do I tell myself if it is T or CT when setting up a channel? In regards to making a quick check on here, and it just lists the PL Tone, how do I decide if it is T or CT based off the info this site lists when looking up a frequency.
T generally indicates that you're transmitting a tone from your radio to the repeater.
CT generally indicates that your not only transmitting a tone from your radio to the repeater, but your radio will also require that tone to be sent back to you for you to receive the signal.
If the repeater you're using requires a tone you'll need to at least have your radio set to "T" for things to work for you. "CT" may work as well since many repeaters will transmit that same tone back to the user (this isn't always the case however). There are even some repeaters that require one tone from the user and will transmit a different tone back to the user, but these aren't too common and normally this will be made clear on the listings for that repeater. Don't worry too much though if your radio won't allow different tones to be set since this is easily handled (see the next paragraph on that).
The need for you to have a tone set on receive is pretty much optional so if you aren't sure about setting a receive tone, simply leave it set for transmit only. This is also a way to handle the repeaters that have different transmit and receive tones if your radio can't be programmed for that. A receive tone can be thought of as a filter. If you have a receive tone set on your radio, you'll only hear stations that broadcast that specific tone, all others will be muted (as in they send a different tone or send no tone at all). It's a useful feature if you have interference from other repeaters that you don't want to hear (and use a different tone) or interference from other signals that make listening unpleasant (such as leakage from cable tv lines, etc.) that won't have the correct tone on their signal. Most digital modes do not transmit a tone so it can be useful to have a tone set on a mixed mode repeater that in analog mode transmits a tone but in digital mode does not as this will prevent you from hearing the digital noise when it's being used in digital mode.
That filter affect is often why a repeater will require a tone. Since they're on tall towers, tall buildings, or other locations that allow them to hear stations from long distances, the tone will help them retransmit only stations that intend for them to retransmit their signals. They may hear stations on the same frequency attempting to use other repeaters and assuming that the tones are different, they will not retransmit them.
Having your radio use a receive tone may cause you issues in some situations. The most problematic one is that some repeaters drop the tone requirement during emergency nets such as Skywarn nets. This is to allow folks that have old radios without tone capability to participate and weak signals may not have sufficient signal to let the repeater lock onto the tone, but they may have important information for that net. Also some repeater operators allow use of their output for simplex operation at times when the repeater isn't operational (often during those same emergency nets) as a backup mode. Many operators do not send a tone when operating simplex (although there's generally no harm in doing so) and if you require a tone, you won't pick up their transmissions.