Please explain everything about multiple regression model?

I do not understand this at all. I'm taking intro econometrics and just did a midterm on simple regression models and calculations and i'm pretty sure I failed. So I need to know everything about multiple regression like what is e value and why are there different variations for e estimator and b estimators, why is there a separate variance for explanatory variables? Can you give a link which explains all the basics about this topic? Should I buy a dummies book? I'm using the book required for the course (principles of econometrics). I need a really good mark on the final. Please help...