How do you know where to start as a beginner that is inflexible. It seems like all of the guides really hurt when I try to follow them.

It is important to not strain yourself. You can always adjust stretches to your own flexibility. Try figuring out which muscles are stretched in the exercise. Try with easy stretches such as reaching up high, crescent moon pose, calf stretch, balance on tiptoes. Use props like a chair or if you have a yoga block to stabilise yourself. The poses shouldn't hurt, only feel a bit tense. Try to internet search for "pose name" + variations. You might find a few. Good luck I hope this helps.

Siempre hay que empezar escuchando a tu cuerpo e ir poco a poco.
La respiración y la constancia son clave.
Detenerse cuando duele, respirar y esforzarse un milímetro mas