Hi. I need some help !
How to join a circle toi a square to make a complexe volume ? (in french version !)
Could you give it a try with CurveBoolean ?
What @jessesn wrote.
As the word ‘volume’ was mentioned in the OP’s post… Do you want to create a surface transitioning from a circle to a square? In that case you might want to investigate the Loft command.
in that case also see: Blending a square and a circle
How will the volume be manufactured? Manufacturing requirements can dictate how the shape should be created. For instance if the shape will be created by bending or rolling sheet metal then the shape should be “developable” which is a different shape than shown in Helvetosaur’s post above or the thread Gijs referenced.
Developable shape created by splitting the cicle and using Loft:
Are there any other constraints or requirements? For example tangency or curvature continuity with adjacent surfaces?
Hi.
Thanks for your answer. The function “Loft” does not exist in the french version of Rhino 
So, I try to find wich command would operate to have the same result.
I tried “balayage1” and “SurfaceParSections”… But all these seem to be mor complicate
So, I would like to know wich french command to as your “Loft”…
Yeah ! Great ! 
A thousand thanks! It’s great! 
It is indeed SurfaceParSections…
Merci 
just type english command name with underscore:
_loft
Hi.
Wich command did you used for this please ?
Hi.
Wich command did you used for this please ?
Probably CurveBoolean
Like @Edr said, CurveBoolean.