You can associate an order with the customer that made the purchase by mapping the customers email address. To do this go to the Data Mappings tab and click the data mapping you're using for your import.

Once you're on the Data Mappings page, select the email field on the Order Details page.

Click the checkbox to the left of the email Shopify field and add the name of the column in your CSV that has the customers email address. From here you can save your mapping and start your import.

After your import has successfully completed you should see the orders you imported on the Shopify Customer Profile page. You'll also see the Lifetime Spend and Average Order. Below these metrics you'll also see the most recent orders made by your customer.