Can I design a structure in STAAD and then import it into REVIT? What kind of functionality will it have? Can I then use the model to automatically create steel details?
Yes, use integrated structural modeling (aka ISM). There are a few details here: https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/3332/integrated-structural-modeling
In a nutshell, you'll install the iTwin Analytical Synchronizer (formerly the Structural Synchronizer) which is free. With that installed, you'll export an ISM Repository, which is a sort of neutral 3D cad file, from Staad.pro. Then install the ISM Revit Plugin and import said file in Revit using the installed tools.
See also: How can I find the ISM installer?
Thanks!