It solves two differential equations and plots the solution for them.
[t,x]=ode45(@rlcckt,[0 1],[0 0]);
ode45 integrates the system of differential equations (the ODEs are specified in function rlcckt) from t=0 to t=1 ([0 1]) with inital conditions [0 0].
You can read about it at: https://in.mathworks.com/help/matlab/ref/ode45.html
plot(t,x(:,1),'m');
hold on plot(t,x(:,2),'b');
legend('x1','x2');
Here, you are plotting the two solutions in the same figure with time in the x axis.