Christian colleges, like all colleges, outline rules for conduct, behavior, and substances in a student handbook that is usually required reading for students before they are permitted to live in the dorm. Many schools require that students sign a copy of the handbook (often a virtual signature) to ensure that students have read, understand, and agree to the rules and regulations the school enforces.
As far as lifestyle and behavior go, each school will have different restrictions and expectations. Christian colleges, especially, will typically have a ban on all substances on campus (ie. Alcohol, drugs, or other). Many Christian colleges will have some sort of rules about what sort of social media posts they tolerate from students who are currently enrolled in their school, but the specific rules for that can be tricky.
The purpose of the restrictions and expectations that Christian colleges outline should be to foster an environment for spiritual growth and Christ-likeness for their students. Keep in mind, while some of the restrictions may seem excessive, they may have more to do with empathy for students who have struggled in certain areas than they do with controlling other students' behavior.
To find out what specific restrictions or expectations a Christian college has, look on the website of the specific school to find a copy of the student handbook or ask the admissions department about it.