Depending on what type of curve you are trying to make, there are a variety of plugins you can use. All of which are very easy to use.
Bézier Curves by Crazyman32 — great for making smooth bézier curves for things like winding roads.
Oozledraw by Oozlebachr — useful for making curves that rely on gravity. Ropes, zip lines, cables, etc. I would suggest checking out a newer plugin of the same type that is still under development but seems to be superior: RopeMaster by XAXA
Archimedes Two by Scriptos — My personal favorite, good for anything you want to create curves with.
Ultimately it depends on what type of curves you are trying to make, but as a builder I frequently use a combination of all of these.