Curve Modifier "disabled?"


I can’t seem to make the curve modifier work. I’ve been doing some blender tutorials from this site and youtube.
I’m currently trying to learn the curve modifier but can’t make it work. I follow the tutorials to the letter but whenever I try to use the curve modifier; the name (curve modifier) is highlighted in red, the “curve object to deform with tab is blank” and when I try to click apply, it says “modifier is disabled skipping apply”

The tutorials don’t encounter any problems before this and I can’t seem to find a solution online.
Please help.

Thank you

You haven’t shown all of the outliner window !
What type of curve have you added. The object box in the modifier will only accept bezier or nurbs curves.
Supply a link to your blend file

Also, the curve modifier only works on a mesh with more loop-cuts. The object you show in your screenshot has only the vertices at each end and, of course, you can’t curve a line joining two vertices. There has to be at least one subdivision somewhere along each line that makes up the length of your object.