the question is if i need to connect my keystation 49 to my interface tascam us -122 to make it sound ????
i already connect it to the usb port of the computer ???
However the notes don't come out ???

please help to that ??
what do i need to make it sound ???

I'm not sure what a keystation 49 is, but I'm gonna assume that it is just a midi controller... If it is just a midi controller, it won't make any sounds, unless you have it controlling a synth module, or a virtual instrument in your computer. If it is an actual synth (makes sounds all by it's self) then yes you will have to make bothe an audio connection (audio out ports of the keystation to a audio in channel on the tascam), as well as a midi (USB connection tp the computer) to get it to work correctly.

i use the keystation 49 2 ways. first i use the midi out to a module and from the
module i use midi thru to the tascam 428 midi in. then just select a plug in

also the keystation 49 is a midi controller. there are know audio outs

I have the Oxygen 8, which is a smaller version of the Keystation. You just have to connect it through the USB, you don't have to use the midi out. However, you have to set up your software right for it to actually make any sound on the computer. If you read the manual for the Keystation and the manual for your software you are using it with it should explain how to set it up. However, I have found that it can be tricky to set up. I've gotten mine to work, but it seems that I have to play with it for a while to get it running correctly. I think it's a setting in OSX as I'm running into the same thing in Cubase SE and in Printmusic 2004.