DUMMIESAs far as best ebook/pdf book version of excel is concerned I'll recommend you to go for dummies.eg.Excel for dummiesFormula and functions for dummiesExcel power pivot for dummiesFinancial modeling in excel for dummiesDuring my initial stage of career I had read above books of DUMMIESAnd ofcourse you can get the free pdf version of books on internet.Thanks Amandeep Kumar for A2A.NP.