Rules trigger on events. Technically only one event can occur at all times. Every further logic goes inside the rule. Example:
rule "Garage Lights"
when
Item Daylight changed to OFF
then
if (Night.state == ON) {
sendCommand(Garage_Left, HSBType::GREEN)
sendCommand(Garage_Right, HSBType::RED)
}
end
For Night and more logic examples have a look Sun (raised / set) indicator - #7 by ThomDietrich