When you mark a drive or folder as sharable you have the ability to say which protocol(s) it should be shared via - AFP, SMB, NFS and FTP. Since the remote machine is another Mac, ensure that AFP is enabled.
So you have to use Server.app to ensure the appropriate service is enabled and running.
Once you've done that you can go to the Finder on the remote computer and choose Go -> Connect to Server. Here, enter the hostname of the server. Since you're using AFP you don't need anything else since AFP is the default, but if you were using a different protocol you'd need to specify that here.
When you connect you'll be asked to authenticate - this is a valid username and password on the server machine, which may or may not be the same username and password on your own machine. Once authenticated you'll see a list of available sharepoints which will then mount on your desktop.