This verse describes Ezra's reaction to the news of the Israelites intermarrying with foreigners, a practice forbidden by Jewish law. Let's break it down:

"and lodged there": Ezra likely took refuge in a specific location, perhaps a temple chamber or a designated area for mourning. He isolated himself in response to the distressing news.
"and did eat no bread nor drink water": This describes fasting. Abstaining from food and water was a common expression of grief, repentance, and mourning in ancient Jewish tradition.
"mourning for the great iniquities of the multitude": This explains the reason for Ezra's actions. He's deeply saddened and distressed by the widespread sin ("iniquities") of the Israelite people ("the multitude"). The intermarriage was seen as a violation of God's law and a threat to the purity of the Jewish faith.

In essence, the verse depicts Ezra's profound grief and distress over the Israelites' disobedience to God, expressed through a period of fasting and mourning. He is so affected by their sins that he isolates himself and refuses sustenance as a sign of his deep sorrow and repentance. This sets the stage for his subsequent efforts to reform the community and restore adherence to Jewish law.