For a refresher tutorial or quick look up on INDEX and MATCH Functions in Excel, ExcelIsFun on Youtube explains it very clearly with great examples.
His explanation is clear and the examples are real-life and practical enough to let you understand the concepts pretty well.
He has done a good job to also provide free practice Excel Practice workbooks which you can use whiles following along with the tutorials. The workbooks can be freely downloaded from here:
ExcellsFun free Excel WorkBooks
You can watch the INDEX and MATCH tutorial from below or you can check him out on Youtube
Happy indexing and matching!