Any one can explain those difference?
Here is what my understanding:
Check out: you can only check out to a workspace
check out to workspace: don't understand this one
add to workspace: create a copy to workspace, there is no link between copy in workspace and file in the Windchill
Check out: Copy of file is placed in your active workspace and checked out.
Checkout to Workspace: Copy of file is placed in the named workspace and checked out, may not be your active workspace.
Add to workspace: places a copy of the file in your workspace, does not do a check out.
In all cases Windchill knows the status of your file and its check out history.
This may help explain Save As:
That's from the online help topic.