first...heavy clean
flashing green return for landing TO BE FOLLOWED BY STEADY GREEN FOR LANDING CLEARANCE
Steady RED while in the air means continue circling and give way to everyone else.
it is likely that if you get flashing green it will VERYsoon be followed by landing clearance
if you get steady red you could be there all day as in maybe the runway is damaged.
for NOW ,just memorize it by rote. NOTHING is wrong with ROTE memorization, full understanding will come with experience.
someday you might even learn about RED RIGHT RETURNING and you can ask about that. but just learn the stuff, and understanding will come.