The description tcpwm.line[X]:Y means
This pin can be connected to the line terminal of the Xth TCPWM block.
And this is the Yth pin where the TCPEM.line[X] can be connected.
Is it hard for you to select a pin which can be connected to the line terminal?
Don't worry. PSoC Creator provides a list of pins which can be used for the line terminal.
Thank you, Noriaki! Excellent answer!