Thought I'd pop in and send you towards some videos I found useful for when I was trying to get circuits down. Some of these are a little old so they won't cover everything but they'll cover most of what you need to know,
General Circuits;
"Factorio Circuit Networks Explained in Under Three Minutes" - DoshDoshington
"The Circuit Network & You | Factorio Tutorial" - Yorven
"CP Factorio" - Center Pivot ;Note, this is a playlist of eight videos. It's for more complex circuitry like memory cells, latches, and flip flops. Still useful.
Examples of what the circuit network can do;
"Building Circuit Abominations in Factorio" - DoshDoshington
"Examples of CIRCUIT NETWORK in Action | Factorio Tutorial/Guide/How-to" - Nilaus
Specifically addresses circuit network changes in F:SA;
"EVERYTHING new about Combinators in FACTORIO: SPACE AGE!" - Center Pivot
Also, here's a thing to remember for circuits (and programming); DON'T FEEL BAD MODIFYING OTHER PEOPLE'S CIRCUIT DESIGNS. Look at other people's circuit creations. Test circuits, see what happens and how the circuits react then figure out why they react like they do.
If Ooba is fine with it, I'll list some mods that're useful for debugging circuits and the mods I use to ease circuit designing
