SnapGene 9.0 and later has a built in primer database. See the following articles to learn how to use the SnapGene primer database:
For older versions you should export your primers to a delimited list.
In SnapGene 8.2 and earlier, view a target sequence and use Primers → Import Primers from a List to add matching primers to the target sequence. See this User Guide article for more information – Import Primers.