You can learn almost anything on Youtube.com My two favorite channels for learning about electronics are W2AEW's channel, https://www.youtube.com/user/w2aew, and EEVBlog, https://www.youtube.com/channel/UC2DjFE7Xf11URZqWBigcVOQ. Here's a nice explanation of dB: https://www.youtube.com/watch?v=1mulRI-EZ80 73, Ian N8IK