The Khan Academy is a non-profit organisation that provides a range of YouTube videos, typically on mathematical themes. It also provides a number of videos on financial topics, which is of more interest to a DIY Income Investor.
Here is one explaining very clearly the inverse relationship between bond price and interest rate - which can, initially, be a difficult concept to understand.
I am not a financial advisor and the information provided does not constitute financial advice. You should always do your own research on top of what you learn here to ensure that it's right for your specific circumstances.