Drawing vertical lines in MATLAB

I am trying to draw 6 vertical and 6 horizontal lines on an image that are crossing each other and form cells. I am new to MATLAB and find it very confusing to find the right indexing.

So if I write the following:

f(60:60:end) = 255;
imshow(f)

I would get some vertical lines, but it is not the desired effect. Any suggestions?