Unable to import public SSH key into WinSCP for remote connection

I am trying to connect to a remote SSH / SFTP server and was given a user name and a public SSH key (.pub file). There is nothing coming up when trying to connect that asks for a key, but it does ask for a username and password. I do not have a password because I was given the SSH public key. Is there a procedure that you can point me to that explains how to import the public key into WinSCP for a specific connection? The documentation on your website talked about generating the key pair. In our example we were only given a public key and do not have access to a private key as we are the "client" logging into their server. I've literally dug through every menu option that I can find in the application with no obvious way to import a public key into the session I'm creating. Please forgive me if this doesn't make sense as I am new to the SSH / SFTP process.

We are currently running version WinSCP Version 5.11.1 (Build 7725) (OS 6.3.9600 - Windows Server 2012 R2 Standard)

You cannot authenticate with a public key. You need a whole key pair.
Possibly the public key you were given was actually a public key of the server, not a key for authentication.
See https://winscp.net/eng/docs/ssh_keys