linestyle and gridlines

[chris]

I started out searching for a way to make my grid lines thicker or
darker so my students could see them more clearly using a projector. I
still haven't figured out how to do that, so any help would be great. In
the process, I noticed the linestyles and linewidth commands, but when I
type linewidth 2 or linestyles : nothing happens. Am I misunderstanding
how to use these commands? do they have to be included in my plot
command? any help would be much appreciated.

Thanks
Chris