C(:,s) = g(:); what values of g will be stored in C(:,s)
All values of g will be stored. If C is not initialized yet then numels(g) will define the number of rows to be created in C. If C is already initialized then if numels(g) does not match the number of rows already in C then you would get an error.
how it will be stored in C(:,s)?
g(:) reshapes the entries of g into a single column vector. The order in the column vector is the order that the entries originally occurred in memory. MATLAB stores in "column major order", so g(1,1) is followed by g(2,1) then g(3,1) and so on down column 1, and then immediately after that in memory would be the first item of column 2, g(1,2), then g(2,2), g(3,2) and so on.
will this colon differs for every new line?
I do not think I understand the question, but, No: see what I wrote above about if C is already initialized. You would have to have the same number of total entries in g in order to do the storing. This does not require that g have the same shape each time. For example,
g = [1 2 3 4]; C(:,1) = g(:);
g = [1 2; 3 4]; C(:,2) = g(:);