Hi and welcome to Scarleteen, hello_world!
The stereotype that cis men intuitively know what brings them pleasure really sucks, yeah, because it is absolutely not true for all cis men, or for people with penises in general. You're not alone, by any means. I'd recommend taking a look at this article for the basics of masturbation: Going Solo
, and there's a number of other articles linked to that one that you may find helpful wrt the mechanics of the process.
Now, as you'll read on there, your physiological arousal doesn't hold a candle to the role that your brain plays in sexual pleasure, especially during masturbation. Given your circumstances (privacy and time issues, depression, sexual attraction not being a possibility for you at the moment), I understand that it may be difficult to get into a mindspace that's conducive to consistent arousal. Self-pleasure depends on all these things much more than it depends on blood flow to the penis, unfortunately. Knowing what gives you an erection is a start, though, and building up from there is possible. What do you do, usually, to obtain an erection and pre-ejaculate? Do those sensations stop feeling good or having any impact after a point?