When you link, you are using a field that is common to both tables. Crystal Reports uses the link to match up records from one table with those from the other. In this example, the link assures that the data in each row of the report refers to the same gift.
Link from and link to:
When you link two tables, you link from one table to another table. The from table is used as a primary table, while the to table acts as a lookup table where records are looked up by the primary table. In a simple link, the Report Designer examines the first record in the primary table and finds all matching records in the lookup table. Once all matches have been found in the lookup table for the first record in the primary table, all matches in the lookup table for the next record in the primary table are found.