There are six steps in the mechanism of TFIIB action in the formation of the PIC and transcription initiation: 
#RNA polymerase II is recruited to DNA through the TFIIB B core and B ribbon.
#RNA polymerase II unwinds DNA, aided by the TFIIB B linker and B reader (open complex formation).
#RNA polymerase II selects a transcription start site, aided by the TFIIB B reader.
#RNA polymerase II forms the first phosphodiester bond.
#RNA polymerase II produces short abortive transcripts due to clashes between nascent RNA and the TFIIB B reader loop.
#Extension of nascent RNA to 12-13 nucleotides leads to ejection of TFIIB due to further clashes with TFIIB.