can anybody explain this function? what is the meaning of Q(1) ,Q(2)?

function [h]=sensor_view(Q,radius)
x=Q(1);
y=Q(2);
theta=Q(3);

[Stephen23]

That is very basic indexing. Indexing is one of the most simple and fundamental concepts of using MATLAB (and many other computer languages). You can learn about indexing by doing the introductory tutorials:

https://www.mathworks.com/help/matlab/getting-started-with-matlab.html