Alpha focuses on teaching you the basic moves (high knees, squat jumps, push-ups, tuck jumps) without the high impact of later phases. It includes a "modified version" athlete (Tania) who shows low-impact alternatives.
You cannot just pick random videos. The program is a calendar. Here is a sample : FOCUS T25 Workout
Each workout follows a "no-break" philosophy where movements change constantly to keep the heart rate elevated. Dynamic Sequencing: Alpha focuses on teaching you the basic moves