Affirmative consent policies in a college sexual misconduct case involve what will constitute consent between parties. When parties engage in intimate or sexual interactions at college or otherwise, as long as they're under the jurisdiction of their college sexual misconduct policy, the question of whether, say, a party had consent to engage in a certain sexual or intimate activity often would come into question in a sexual misconduct case.
Affirmative consent is that a person has to obtain voluntary knowing conscious consent or agreement to engage in a sexual or intimate activity with the other party. It could be done through either verbal or physical means, say by spoken word, "Can I do this to you?" If the answer is yes, then that would be affirmative consent. Even something as arguably benign as kissing, if a person leans into the other to kiss and the other reciprocates, that would be, or should be considered affirmative consent. It can be very nuanced and consent is often an issue in a college sexual misconduct case. As to how to best defend against allegations of there being not consent, you need to have an experienced attorney advisor in your corner to help best present what needs to be articulated so that consent can be established.