There are at least two important ways in which the Crusades led to the modernization of Europe.
First, the Crusades reduced the prestige and power of the Catholic Church. This led to more power flowing to the monarchs of Europe. This, in turn, started to lead to more modern forms of government.
Second, the Crusades exposed Europeans to vast amounts of knowledge that they had lacked before. During the Middle Ages, the Middle East was the center of learning and knowledge whereas Europe was relatively backwards. Through contact with the Middle East in the Crusades, Europeans came to be aware of many new kinds of knowledge. These things also helped to modernize Europe.
Please follow the link for a detailed list of some of the things Europeans learned from the Middle East.