"I often feel like I ignore his testicles but I'm worried I'll hurt him. What can I do?"
I often feel like I ignore his testicles in favour of his penis but don't really know what I'm supposed to do with them!
I've also heard they are incredibly sensitive and am worried I'll hurt him.
Testicles are a bit like breasts: some women love it when they are squeezed hard, others shoot through the roof.
So definitely start with a gentle touch and then experiment from there, asking him what pressure he likes (and not getting in a huff if he says he'd prefer you don't touch them at all).
As for what to do, play with them during oral sex or a handjob and also try reaching through to squeeze them during intercourse.
Try cradling them both in one hand, then circle the flat palm of the other hand over the surface. Alternate stroking with fondling and massaging.