A VORTAC is a combination of a VOR and a TACAN, that are installed at the same location.
The frequency that is written next to it is in fact the VOR frequency that you can dial.
The channel that is written next to it is the TACAN frequency that only military aircraft can dial.
A TACAN station always has a DME, which works in the same way as a civil DME therefore if you carry DME equipment in your aircraft you can also tune to it and you have the same information as a VOR/DME.
A VOR and a TACAN work in a different way but the cockpit indication is the same, both send out radials. The VOR works in the VHF range (108-117.95 Mhz) while a TACAN works in the UHF frequency range.
A VOR station is in fact a very large (I estimate about 20m radius) fixed installation while a TACAN is quite small and can be made mobile.
The TACAN has as advantage that it is small and can be moved around, which is very interresting for the military. The disadvantage of a TACAN is that it can have a fourty degrees azimuth error and the cone of confusion is much larger than that of a VOR.
A TACAN looks like a barrel, in the middle (inside the barrel) you have a fixed antenna, and another antenna rotates around it.
In a VORTAC the TACAN is often installed on top of the VOR.
On the picture below you see a VORTAC, the VOR is the large circular construction and the TACAN is the white barrel on top.
Picture courtesy WIKIPEDIA
Bart