Robert Lie Mobilefish.com has created a series of 53 video tutorials on YouTube explaining LoRa & LoRaWAN. Most are short (<6 minutes) and well indexed, so you can quickly find topics of interest. Many illustrations and demonstrations of LoRa signals on SDR displays. Highly recommended. Complete playlist at https://www.youtube.com/playlist?list=PLmL13yqb6OxdeOi97EvI8QeO8o-PqeQ0g

He also published documentation and slides at https://lora.readthedocs.io/en/latest/

Andreas Spiess also has a LoRa / LoRaWAN series of maker projects on YouTube at https://www.youtube.com/playlist?list=PL3XBzmAj53Rkkogh-lti58h_GkhzU1n7U