example with ' through point ' command ( in yellow )

pick points on your sketch or object and the curve is made ... right click to end

go to top view to be sure your curve is flat ... on an object ( if you draw in front view ) you can hasardously pick on points that are not in the same plan

use manipulator around your curve and move a corner ... you'll see the word ' Flat ' when all the points are in the same plan

( not sure my english is orthodox !!! ;)