You can import a .csv file of your Contacts if you wish. The file you use should contain header rows and you will map your columns in the spreadsheet to fields with SI. If you would like a template .csv file in which to paste your data, you can enter one Contact manually in SI and then Export->CSV->Selected:
You can then delete the record from the spreadsheet and use this template for your import since all columns will automatically mapped.
You will need to map the columns in your CSV file to Contact Fields in the SI. Some fields will be pre-mapped if they are an exact match or if they are a close match. When you click the Map button next to an item you will then be able to select the appropriate field or you can unmap any field by clicking the None button on the form:
Select the Clients you wish to import then click the Import and Close or Import button: