Grasshopper .. how to import from rhino some object .. for example a curve to grasshopper

how can I put from rhino some object … for example a curve to grasshopper ?

I’m a beginner … but this is so a fundamental thing and a can’t find something like this ?

is there a function in rhino … like export to grasshopper … than this objekt could change to a special object with which you can work with in grasshopper an return a result ? Choosing if you want to make the input visible or the output from grasshopper ?