which ip do use to set up my ftp ip? my pc or mycloud ip
For the single bay/single drive My Cloud you enable the FTP option in the My Cloud Dashboard.
Once enabled any local network FTP client can access the My Cloud using the local network My Cloud IP address.
For accessing the My Cloud FTP from a remote location one would have to configure port forwarding of the FTP port in the local network router to pass the FTP port traffic from the internet to the My Cloud (IP address). Once port forwarding is properly configured one would use the broadband IP address of the network the My Cloud is on in their remote FTP client.
One can find their broadband IP address (when on the same local network as the My Cloud) by accessing sites like https://whatismyipaddress.com/.
One note on security. FTP is an insecure protocol. Generally the username and password used to access the FTP server is passed in the clear and can potentially be intercepted.