There are two main ways we experience colour in things. Things which give off light use additive mixing: red+green=yellow. This is what RGB colour is, where the primary (or base) colours are red, green, and blue, and is how screens work. The more light you add, the brighter it gets. Add in all the colours, and you get white.

Then we get subtractive colour. Instead of stuff giving off light, everyday objects will reflect some light and absorb other light. A red t-shirt looks red because it gets hit by "white" light (or light of all different colours) and absorbs everything except the red. It reflects the red, so we see it as red. As it happens, one of the easiest way to mix colours in this space is using cyan, magenta, and yellow as the bases - the primary colours. These are the exact secondary colours of light, the additive colours. The more of a pigment you add, the darker it gets. If you mix all three, you get black...sort of. It's tricky to get a really good black, so in printing we tend to just use a seperate black to Deal with that. We call this CMYK (with K being black, obviously... /s).

Now, Pantone is designed to be a system for getting really good printed colours which can be used across different manufacturers. You can think of it as being a sort of translation between colour schemes. Another side of this problem is that computer screens can only produce so many colours. The Hex system you mention means representing each RGB pixel with 3 values from 0 to 255 (one per colour), with 0 being off and 255 fully on. That's a smaller number of possible values compared to what our eyes can cope with. This is part of the reason dark videos look so blocky, almost pixelated. When the lightest value in a shadow is 9 and it fades to complete black (0), there are only 10 possible values in that range. So the steps are obvious. But Pantone is designed for ink where you can just dilute colours further and further to get shades in-between.