Apps on apple watch

I have a iPhone X and just bought a se Apple Watch I haven’t set up the cellular on the watch yet and I thought when the watch and phone are together I could use apps on my phone on the watch but tried to download Afterpay on the watch but I can’t and also a COVID checkin app , do they not work using my phones internet or do they only work if you have the cellular set up, any help would be welcomed as I didn’t want to go on a plan with cellular for the watch until I see if I like using the watch.