Ok so the bass and kick drum just need to have the same polarity? Even if they are not time aligned? I will be honest, I have never paid attention to the polarity of my recordings in this way. Should I?
No, no particularly. :) You can try and see what happens, but that's it, outside the specific case below.
It's easy to understand if you think of two sine waves of same periodicity, plotted against X and Y axes, where Y is amplitude and X is time. Look a the points X where the sine waves start (i.e. Y=0) and where the crest and valley are.
The waves are relative phase if they start at the same X: if summed, the resulting sine wave will have higher amplitude (i.e. be "louder" if the wave is transduced by a speaker).
If the two X are as far as they can get (i.e. the peak point of the first wave is where the second one has its valley), they are in opposite phase (or "out of phase") - the sum will have shorter amplitude (i.e. be "quieter") and even cancel out completely if the waves have the same amplitude.
For all the other relative starting point position, they will be a bit in phase and a bit out of phase - depending on how you prefer to look at it.. if the starting points are near to each other, they're "mostly in phase", in they are near the "opposite" position, they're "mostly out of phase".
To change the relative phase, you simply delay one of the two waves a little bit - nudging it in time.
Obviously for more complex waves, and even sine waves with just different periodicity, they will be almost always in this gray area and things will shift all the time from "mostly in phase" to "mostly out of phase" very fast - in other words, a normal interference pattern which results in specific timbres.
"Polarity" is just where's the north and where's the south. The Ø button simply flips north with south, so if you push it on a channel, you will flip the corresponding wave, changing the timbre of the summation.
Of course in rare cases where the sound waves are very similar (say bottom and top mic for a snare, the snare component in the overheads and the snare mics etc) and they happen to be mostly out of phase (it will never be exactly so of course unless you duplicate a recorded sound), that button is a quick way of nudging one of the two to get them mostly in phase. It's just a shortcut to get in the ballpark, instead of inserting a delay (which, I guess, used to be a quite complex thing with desks and physical inserts).
Otherwise, you're just gonna change the interference pattern - aka the timbre.
It can be nicer, it can be worse - it all depends on your taste. It's worth trying to see how it changes, but it's nothing you have to do or otherwise critical. If you have timbres you like, you're all set.