#1
so, certain musical equipment (keyboards/mixers/etc) have midi input and output.

like this




and my question is: is it possible to somehow connect this directly to a pc? Like through usb or the midi of the sound card? So I can use various midi soudfonts/effects etc.
Dear God, do you actually answer prayers?

Yes, but only in a way indistinguishable from random luck or the result of your own efforts.
#3
There are several Midi to USB adapters that you can buy. Most of which are small boxes which have midi in/out cables at usually come with software to configure settings through. Those are the somewhat nice ones, anyway. Most of the nicer hubs, though, that I would recommend are ones that are USB audio hubs, which you can usually control through your own sound card's configuration, and force it through. That usually can be a bit nicer, depending on your setup.