Hi boja, maybe you're getting confused since things are structured slightly differently in MoI than in Rhino - in Rhino there are different commands for blending curves versus blending surfaces, while in MoI there is just one Blend command which can work on either curves or surfaces depending on whether you have curves or surface edges selected when you run it.

So you use the Construct > Blend command as shown above to do what you want, just select curves as the input objects for doing the blend.

This type of combining of both curve and surface processing functions into just one single command rather than separate ones is one of the ways that helps keep MoI's UI to be more streamlined and not get so cluttered up.

- Michael