QuickBooks should be open prior to importing Vendors. This is not required but speed will be improved.
You can click the check box next to multiple Vendors to import them into SI 2018 or you can use the [Select All] button on the ribbon.
There are column filters:
There are filters in the ribbon for showing All, New, or Matched Vendors. The New filter shows only Vendors who don't already exist in SI 2018. The Matched filter will shows only Vendors that already exist in SI 2018, use this for updating information for existing Vendors.
There's a search field: