Learn how to use the bezier tool in 3 steps! The bezier tool will help you make great lineart and perfect curves. :)
In the first step, just draw whatever. I drew a simple cloud looking curvy thing, with very messy curves. You could draw a anime sketch if you want, it works great for that :D
Now at the top left of you're screen, where the brushes are, select the bezier tool. Its the very last one. Click one end of your curve, then click the other.
Now move you're mouse near your first point, and move your mouse around until part of you're bezier is touching a high part near your point.
IMPORTANT: do NOT click the highest point of the whole thing, so don't click in the middle or it wont work.
Last step! ^^ Now on your second point, move you're mouse until the bezier is outlining your shape, then click!
As you can see I have done the rest of the curves. If you are doing lineart you can delete your sketch now! :D I hope you enjoyed my tutorial and that you now understand how to use the bezier tool. :)