I bought a template and I am editing it. However, I want to create some straight lines on the document and the line segment tool greyed out? Any idea why this is or how to correct it?
Have you tried the Pen tool?
I suppose you clicked on the 3 dots in the tool panel?
Don't do that unless you want to configure the tool panel itself.
If you need more tools go to Window > Tools > Advanced
You can just exit the configuration mode and use the line segment tool.
I can't produce a situation in which the line segment tool is disabled ('grayed out'). Even when there's a dialog open and all the tools are unavailable, they don't "gray out".
It sounds more to me like something else has stolen focus from Illustrator, or you need to reset preferences.
mine was greyed out too. It seemed to magically appear after some haphazard menu journeys that I didn't properly log in my journal. My ellipse tool (and many more visible only via the 3-dots button) are still greyed out. How does one actually access the ellipse tool? Can it be added to the basic or advanced toolbar? The lasso tool and symbol sprayer tool are readily accessible, but creating lines and circles seems to be reserved for advanced users.