Transcription starts with an enzyme, called helicase, which opens up the DNA molecule (separate the two strands). RNA-primers will then locate a site in the DNA which is the site that codes for a protein. These areas are inbetween a series of bases which tells the RNA-polymerase to start or stop adding bases. RNA-polymerase adds nitrogenous bases in an order, complementary to the template DNA strand, except that the base T is replaced with the base U.
When the transcription is over, the mRNA strand that was just made is carried out of the nucleous, and it will find a ribosome to which it can bind and create a protein (translation).
Hope this was any help.