Clicking on the People > menu item on the left and side, you will see an Import menu option.

Here in the Import pane, you can import a CSV file containing People you want to add in bulk. 

Do note that this tool is not intended to upload 1000's of records. If you need to do very large imports, you should use Bridge.

To import, you must first either drag your CSV file to the box at the top, or click on the box to open up a file explorer, and select your file.

Once you have selected the file you want to import, you will see a preview of the data show.

Below the preview, you have three buttons: Cancel, Configure, and Upload.

Before uploading the data, you will first need to configure the mappings. To do so, click on the Configure button. A new pane will open allowing you to see your field headers on the left side, and a list of dropdowns to select the correct field in Controller on the right side. Be sure to check all of the mappings, and select the respective field you want the data to be stored in.After a field is configured, you will see a green check mark to the left of the field in this window.  If you want to remove a mapping, click on the X button to the right of the field. Click on the Save button in the bottom right.

Now that you have all of your fields mapped, you can click on the Upload button to send the CSV file to be uploaded. You will see it give a notification for every 10 records that it successfully uploads. 

If for whatever reason the import fails, you will see a notification, and a red Errors List button will appear. You can click on the Errors List button to get an idea on why the import failed. Then correct your data, and try the import process again.