Information about usage of threads in ISE Eiffel is contained in the EiffelThread library documentation. In this section we will only see what is required to enable threading at the level of the compiler options and how to create special type of onces: global once versus once per thread.
Users of the EiffelThread library in version 4.5 and older should read "changes between 4.5 and 5.0" to get the info they need to migrate their code to the new implementation of threads in Eiffel.
If you encounter problems, have a look at the FAQ list.