[Elecraft] K3 Internal Keyer vs. Straight Key

[KE8G]

Dumb question here!

I have a K3/100 #4401 and I am using N3FJP software.  I just purchased the Serial to Straight key cable. The setup instructions says the internal keyer must be turned off.  I see nothing in the manual on how to do that.

Also, on the rear panel there is an input for paddles and one marked key.  I believe that is for a straight key/PC, etc.

How do I turn off the internal keyer?
Or, can I keep the paddles connected (use when desired), plug the cable in the "key" input and use the software & PC?  Have both connected at the same time?

Thanks in advance,
Jim - KE8G
73