The transition to online learning due to COVID-19 brought opportunities for applying Situated Learning Theory through mobile social media to enhance individual cognitive growth and community sense of belonging in online learning environments. In this study, we invited students from an Environmental Psychology course to participate in a semester-long project, during which they were required to post Instagram photos of their surrounding environments every week. We intend to understand the mechanism of integrating social media (Instagram) into a hybrid class amid the global pandemic, and how the project affects students’ learning experience. Through in-depth interviews with 22 study participants, we found that integrating Instagram into the course helped students effectively connect with both real contexts and their peers. The project enhanced participants’ situation awareness and a sense of belonging through posting, interacting with peers, and browsing profiles and posts. We then proposed a framework of creating a situated learning environment through social media using conjecture mapping to inform design implications and future studies in social and mobile learning communities.