The RT Oral as you put it, is a practical test to see if you can put into practice the same things that you are questioned about in the written paper.
It sounds very much as though you are attempting both of these tests with no training; not uncommon, but not to be recommended from a safety perspective.
The RT Practical test is described in the Safety Sense Leaflet on Radiotelephony which can be downloaded from:
http://www.caa.co.uk/docs/224/ssl22.pdf
It is also published in LASORS.