Leads allow you to track any files relevant to the sales process in one location.  Very handy if a sales person has to take over the process mid lead.

Add or edit a lead and from the lead's detail page, click the Files tab

Click Select files to choose the file to upload.   Add a description and click Upload.

Access lead files by clicking on the file name to download to your device.   If the file is no longer required, click Delete.

Note:  Files attached to emails sent to the lead will automatically appear in the files tab.