If you have created your timetable using the timetable generator you will have a record of the information.
If you have a module clash, you need to change your module selection, or speak to the module co-ordinators.
Using the example RELU911, the first 3 characters represent the subject area, so REL is Religious studies.
The 4th character represents the level of study, so U is undergraduate. P is for postgraduate.
The 5th character can sometimes represent location, e.g. S for Singapore, M for Muscat, H for Hong Kong.
.C = Cottrell Building (e.g. C.LTLogie)
.P = Pathfoot Building (e.g. P.D1)
Macrobert (MH) is the Macrobert mainhouse, the large theatre
Macrobert (PH) is the Macrobert playhouse, the small theatre
Macrobert (FH) is the Macrobert filmhouse, i.e. the cinema