Sometimes it is easier to use 2D sketch than 3D sketch. But that can create problems latter when you try to do something with your sketch. On the picture you can see that I have two sketches that are connected.
If I try to apply a sweep feature on this sketch and I try to use it as a path I get this problem (look at the picture)
The problem is that my sweep path is made out of two sketches instead of one.
That is why we use a composite curve. Under the insert - curve - composite curve.
When we click on it a property manager appears on our left side.
We select both of our sketches and we click OK.
We get one curve like in the picture.
Than we try to complete a sweep, and we are successful.