You can import a file of contacts to your account! On your Contacts page, you can click on the main context menu "..." on the right, and select "Import Contacts":
You can also choose the "From Outlook CSV File" option from the Contacts > Import/Update Contacts main menu:
On the Import Contacts page, there is a "download a blank Outlook CSV File" link to download a sample file that has the good format and headers.
You can also download that sample file by clicking here.
Next, copy and paste your contacts into the sample file, and save it on your computer. For a quick guide to editing your contacts file, and general tips for ensuring that it imports successfully, check out this great video.
Once you've saved your file of contacts, use the "Step 2" area on that Import page to select it, and then choose whether you'd like to "Overwrite" duplicates, or "Keep existing".
Overwrite Duplicates: if the importer finds a contact in the file that shares an email with a contact in your account, the info in the file will overwrite and update that contact.
Keep Existing: if the importer finds a contact in the file that shares an email with a contact in your account, the importer will not import that info, and will not not update the contact.
Next, you can choose a distribution list you would like these contacts to be added to. This is optional, but it's a great way to group those contacts, and be able to market to them later.
Lastly, click "Import File". The import will begin, and you can check the status of it on your My Imports page.