A truly anytime, anywhere approach to immersive analytics is predicated on the ability for users to author and explore visualizations in an immersive fashion and without a desktop computer. In this paper, we present a generalizable visual programming technique for immersive authoring, exploration, and presentation of data visualizations through direct manipulation, and implement it in a web-based augmented reality (AR) system. In a preregistered user study, we use this implementation to explore how analysts author and use data visualizations in immersive AR accessed using a head-mounted display (HMD). The study focuses on the authoring technique, spatial organization strategies, and sensemaking and presentation practices in such immersive analytics environments for HMD-based AR. Our findings suggest that participants particularly liked the direct manipulation of our approach, and that participants' spatial organization is not based on physical landmarks in the room.