Starting yoga doesn't require any special preparation — a bit of floor space, comfortable clothing and a willingness to follow along is enough for a first class.
Wear something you can move in comfortably, avoid a heavy meal in the hour beforehand, and keep a water bottle nearby. If you're joining online, set your mat up somewhere with a little open space around it.
A typical beginner session opens with a short warm-up, moves through a guided sequence of postures, and closes with a few minutes of relaxation. Instructors talk through each posture as it comes up, so you're never expected to already know the pose names.
Morning batches suit people who want to start the day with movement; evening batches work better for winding down after work. Either is a reasonable place to begin — the more important thing is choosing a time you can actually keep to each week.
Flexibility and strength build gradually. It's normal for early classes to feel effortful — consistency matters more than how "good" the first few sessions feel.