adding a legend in 3 for loops with three plots .MATLAB

Question

l want to make a legend for my figure but l have 3 for loops with three plots like mentioned below : legend 1 : essential legend 2 : less essential legend 3 : most important

for P=1:K
   % body 
plot(.....,'bo');
end

for  Z=N:T
  %body
plot(....,'ro'):
end

for  i=1:L
 %body
plot(....,'ko'):
end

how can l manage my legend ? thank you