help slots in montages and what the buttons that change the slots do and why they are used

I’ve been reading the documentation and have been watching videos on montages + slots. However, I still don’t understand the process. For example, the button DefaultGroup.Default slot confuses me , as I don’t understand what it is actually doing. Does it allow only one animation to play? If so then why have animations in the tracks that you are not going to play? It seems to me that I am missing a logical step in my mind about how slots actually work and the whole point of them.In my mind I see people clicking the button to change the slot, which then does what? Do all animations play, or I mean how what action is it actually causing in the track with animations in each row? I just don’t understand I suppose how and why of this, and when to put an animation there if another is only going to play, and what the Anim Slot Manager is doing. Like I said I’ve read the documentation such as here: Animation Montage in Unreal Engine | Unreal Engine 5.1 Documentation and have watched videos but something is not clicking in my head. If someone can explain it in more simple that would be wonderful.