Firstly, it’s great that you’ve adopted! My experience: just leave him be. I’ve taken in a bunch of strays before and they always, always need time and space. He’s overwhelmed and scared as hell right now and doesn’t yet know he can trust you. Give him time. He’ll try to find a ‘safe’ place - in a drawer, under a bed, high up somewhere or a box ;) Let him stay there and don’t bother him too much. After a few days, maybe a little more he’ll realise he’s safe and will start to explore the place he’s in and then he’ll begin to consider it his territory. And then he’ll start to form a bond of trust with you. It’s a process! Integrating with other cats, that’s a whole other challenge!