If you have Channel 1, you can set trigger on edge, and signal is shown on current time scale.
But then for Channel 2, the signal is shown in same time scale, and not triggered to any edge?
Yes. Because you want to see how Sig2 correlates or relates to Sig1. With the same time-base, or frame of reference.
Do some scopes have triggering on each signal individually?
Yes. Dual time-bases have been around a long time. They can be correlated (simply time-delayed, or offset), or independent (alternating).
But how are the signals then displayed? In separate windows and time scales?
Yes. How else could it be? Well, not in a "window" or box, necessarily. But offset vertically, and with their own time axis.
What are the use cases? Isnt there always 1 common reference?
Would like to hear about the different use cases/advantages/disadvantages.
Perhaps you have an event on Sig1, that you need to see in high temporal resolution (say, microseconds). But then there's a 2nd event that follows, a "long time" later (say milliseconds). With a time-delay, you can shift Sig2 so it can be seen with the same high-rez as Sig1, on the same screen. Without it, you can see them both only when zoomed far out, and you can zoom in on only one at a time.
And no, there's not always 1 common reference. With alternating time-bases, a single scope can trigger first on Sig1, then next on Sig2. Back and forth. They alternate, which essentially gives you two scopes in one... though you could get the same result with 2 separate scopes. The downside is that each channel gets only half the # of trigger events, because you've split the scope.
That's all the education I have time to dispense today. Rather than saying "I'm a dummy", why not take a class, or read a book, or spend some time on-line reading? The web these days is a vast cornucopia of knowledge. Not much reason for anyone to say they know nothing, other than laziness.
If you feel you might need this dual-timebase capability, take a look at something like the Rigol DS1052E, which supports it. Along with another feature missing from the current gen of cheap scopes... Equivalent Time sampling. To provide sampling rez of 25 GSa/s, 50, or even more! But only with repeating signals with stable time/phase, which isn't always easy to come by (and possibly why it was dropped).
The 1052E is very cheap, only $329 or less. You could probably find a used one even cheaper, and use it as a "starter scope", to gain some basic knowledge. And exit the "dummy domain".
Then sell it to the next newbie in line, to reap similar benefits. That way you'll be in a much better position to really know what you need/want in a scope, without having spent a large sum of money prematurely.