You find the import feature in Admin->Import/Export->Import
To get started you click on the green Import button
For each different type of Import, you will get a pop-up with a Template file
Start by downloading the Template excel file - this file will give you the correct Columns, in the correct order.
It is very important that you do not change these columns or delete them.
Before you import remember to check the last checkbox.
Make sure to select the correct type of upload - you will get errors if you try uploading the wrong type of excel sheet.
When you work with updating your Style and Item data using the Import Update functionality it is important that you test it out before you start importing.
The best thing you can do is to try any import out with just one or two lines in your Excel sheet.
And make sure to test it on a style that is not super important. Because if you mess up your data - it will be gone - forever. There is no way of bringing it back.
When you think your data is ready for uploading - please try to upload smaller excel sheets at a time, because if there should be any errors it will be much easier for you to find the relevant line where something went wrong.