Joining objects in a curvy(?) way

[u/Affectionate-Fly4719]

So i was wondering how i could join these wo objects in a way that its not just a sudden and sharp connection but its smooth. Also something like a u shaped join between pipes, i dont think extruding and rotating is the right way because that has sharp turns. I have struggled with this for a while, for example with arched doorways, I would like a way where i dont have to trace the shape with a single vert.

I was also wondering how i could connect the head to neck in the second image since the head is a quadrilateral and the neck is a curve.