Machinus

This connector says it can crossfeed, but the fuel doesn't flow. How do I get it to work?

There are 4 stage groups. Third is booster, second is disengage, first is booster, and zero is engines.

Hello, I am new to KSP. I have read the controls, and I am trying to use them as it says in the manual. I am practicing using stages. I have made a 4 stage rocket, in reverse order 3-2-1-0: boost, jettison, boost, engine. When I press spacebar, all stages activate at once. How can I activate stages one at a time?