I started to study ordinary least squares (OLS) estimators and am still at the very beginning. I already bought some books on econometrics but I did not find anything online. So I was wondering if there exists a website, homepage or other online resources that explain least squares estimators in an exhausting way. I am looking for material that provides a general introduction or overview. So far I did not find anything too mind-blowing on the internet. Does anyone have some useful references?
The ideal online reference explains OLS in a simple way for an applied purpose. Ideally, it also provides examples and further information on specific topics, such as the mathematical derivation of the estimator, the assumptions of OLS or mathematical poofs that the estimator is unbiased. I am not looking for a pdf of an econometric book.