You can have a parent product that contains own properties and children products (variations). You can import the child/variant SKUs and relate them to the Parent via CSV file.
Step 0. Create CSV file
The easiest way to get sample of CSV file, create one product via Admin UI and export it to CSV.
Step 1. Set MasterProductId
Use MasterProductId to set the relation between parent product and variations.
Step 2. Import products
Import products. Map
MasterProductId and complete import.