Enable collision for each object you want to interact
Use the transform tools to move the objects
There's special behavior for groups - you don't have to ungroup objects but you can enable collision for sub-parts or the group itself. If you have collision on a parent/group then its children are treated as one object.
Stager does not have live physics - like simulations of gravity, wind, friction etc, yet. It is only exposed through the transform tools. However it is built on a physics engine that we plan to expose more features for in the future!
For a chain, I would make all of the pieces then select them all and move it together. I will say this isn't probably the best case for collision - it's more usful for things like stacking books, putting obejcts on tables or leaning up against eachother. We can make a better interface for something like chains though for sure ❤️