Mail merge allows you to personalize letters by merging recipient information from a database into standard letter text. The process involves preparing the letter template, adding personalized fields for recipient name, address, and greeting, previewing the merged letters to check for errors, and printing or emailing the final personalized letters. Excel can be used to track daily activities and calculate the number of hours spent on each one over a week by listing activities, times spent, and adding formulas to summarize totals.