How does this part of algorithm works?(K-means)

I can't understand the red box. what do does that 1 do before {c(I)=j} ? Also how does all the algorithms work? May someone explains the to steps more clearly by one example!

1_{c^(i) = j} means if c^(i) is equal to j the value is 1 and zero otherwise.
• Is mu(j) a vector? I am confused about I and j. what do counter these 2 letters? – user8663682 Dec 23 '17 at 3:49
• @user8663682 mu(j) is mean of members of the cluster j at each step, and c^(i) is index of the cluster which is assigned to the point of x_i. – OmG Dec 23 '17 at 10:51