Associate pins to stations? (newbie Q)

[noequus]

Hi:

I'm obviously missing something basic as I try to set things up for the first time. SIP seems to be running fine on my pi-4 and I can create new programs and assign them to stations. But I cannot figure out how to assign a GPIO pin to a station. I was assuming I could do something like:

1. Assign any BPIO pin to a station (eg, say...pin 7/GPIO4 to S1)
   
2. Connect that pin to a relay
   
3. Connect that relay to the valve for S1
   

Then, when the SIP scheduler turns S1 on, pin 7 goes high (or low, depending on relay), which activates the relay and opens the valve.

I can't find info on that anywhere....

Eventually, by trial and error I tried adding the relay_board plugin; using the figures in its wiki I got the SIPs scheduler to turn an LED on and off (didn't bother adding a relay). But since that uses an optional plugin, that's probably not the normal way to do things.

I have lots of available pins so don't think I need a shift register (I've never used one of those...though the figure there indicates pins 7, 11, 13, and 15 are important...)

In any case, can someone tell me what obvious thing I am missing? I've studied the wiki and searched the Forum but have found nothing, and nobody else seems to have this problem so I am feeling pretty dumb!

Thanks for any guidance.