Best way to pay for GRT?

So I just moved to Kitchener from Toronto where I used public transit daily. I haven't used GRT yet but I downloaded the GRT pay app and bought a couple single use tickets just to see how it worked. When walking by a bus stop I've noticed most people aren't using their phones, so I was just wondering what is the most common and convenient way to pay when getting on a bus?

Also, how do transfers work? Say if I was transferring from a bus to the light rail?

I've looked it up but it can be a little confusing so I just wanted to get actual opinions.
Thanks in advance!