On step 2 of your letter creation, make sure to set the Create One Letter Per option to either Constituent or Household. Setting it to Transaction will create a separate letter for each transaction. You might also embed the data table into the letter as well. Do this by putting your edit cursor in the body of the letter where you would like to add the table, then click on the Bloomerang logo with the gridlines. This will embed a table into your letter that will list all of the transactions for the constituent or household that you filter for.