I had a little bit of trouble too at the start, Im not that good rn either but I've gotten throught the first few stages!
But what worked for me was holding off on battles for a bit and focusing on training for stats. Your stamina goes up passively and goes up fully if your digimon sleeps for the night so you could wait for full stamina. I didn't use pills cause I thought they were bad too, you can experiment with that if ya like. For me I focused heavy on speed (which makes your digimon hit more often) cause that was easiest for me and did some of the others, if they're too hard click skip to get a few stats (You can get up to 3).I think to make your digimon happier is to just talk to it when you have the option to click on it!Once you've gotten into the like 30-40 range try your luck in random fights, you can run if you think you might lose and your winrate wont decrease but you won't gain a small amount of exp and bits and once you can confidently beat a few randoms try adventure.
I recommend you join the discord for better and probably easier to understand advise cause I don't know much of what I'm doing either XD this got me to champion and on the way to ultimate though in a decent amount of time for vpet standards at least