I assume that you are talking about the Saeculum Obscurum in the Papacy? The short answer is that the papacy reached new heights of corruption and licentiousness that would not be reached again until the reformation. The papacy was, more than ever before, under the control of the various Roman noble families, especially the counts of Tusculii, the Crescentii and the Theophylacts. Basically it was a lot of very short lived, incompetents who squandered the wealth of the church and quite often murdered each other. Some examples are needed to illustrate the confusion and instability of these years.

In one particularly gruesome episode the body of Pope Formosus (891-896) was exhumed by his successor eight months after he had died and was put on trial for perjury and coveting the Papacy. He was convicted, the three fingers of his right hand were cut off and his body thrown into the Tiber.

There are many other colourful characters in this story including Mazoria the "senatrix" of Rome who wished to have her son on the papal throne. She placed two old men there as stopgap measures and deposed John X (she hated him because he had been her mothers lover) when he appeared to be becoming too independent minded. Mazoria eventually managed to put her son John XI on the throne but his mother was murdered and he was kept as the personal slave of his half brother Alberic for the rest of his life.

Stephen VII (939-42) was brutally murdered by Alberic and he appointed the rest of the next five popes including his illegitimate son John XII (955-64) who marks the nadir of the papal pornocracy. Gibbon says that "he lived in public adultery with the matrons of Rome...turned the Lateran [palace] into a school of prostitution...his rapes of virgins and widows had deterred pilgrims from visiting the shrine of Saint Peter". He was eventually deposed by the Holy Roman Emperor Otto of Saxony. The only problem was that Otto attempted to crown his own successor to John, Leo VIII. The people of Rome refused to accept him because he had been forced on them by the Emperor and this led to a really big Schism and then eventually a reformation movement coming from the abbey at Cluny.

"The Popes" by John Julius Norwich has a very good chapter in it called "Nicholas I and the Pornocracy"