1. You do not need to be flexible
That is like saying you need to be clean to take a shower. Flexibility is a result of yoga, not a requirement.
2. Arrive ten minutes early
Grab a mat, find a spot, and let me know about any injuries.
3. Wear whatever you can move in
Leggings, shorts, an old t-shirt. Nobody cares.
4. Rest whenever you like
Child's pose is always available. Taking it is a sign of wisdom, not weakness.
5. Stay for the rest at the end
Savasana is the whole point. Do not skip it.