Session View is the default view when opening Ableton Live. It serves as both an “idea board” for musical clips or phrases as well as a way to trigger those same musical clips for live performance. The workflow here is usually top to bottom.
Tab to Toggle to Arrangement View. Arrangement view is the timeline view that all DAW’s have. The musical ideas from session view can be copied or recorded into Arrangement View to linearly write a song from left to right. You can record new ideas into Arrangement View as well.