Merge 2 Excel Spreadsheets

I have 2 Excel Spreadsheets that need to be merged. Both sheets have 1 column in common -- Account number. The association is 1 to many where many records from sheet 2 need to be merged per account in sheet 1. The goal is to bring all these records or create a new sheet that has all the information from both.

The final product should have the instructions on how to duplicate this by combining 2 sheets into one using this 1 to many relationship.