I’ve lost my contacts and don’t know how to retrieve them

If you are using iCloud, make sure you have contacts set to sync.

Change your iCloud feature settings [iOS and Mac] - Change which apps sync and store data with iCloud - Apple Support

If you accidentally deleted your calendars, reminders, bookmarks, or contacts from iCloud, read this support article --> If you accidentally deleted your calendars, bookmarks, or contacts from iCloud - Apple Support

This article has similar information --> Restore contacts stored in iCloud on iCloud.com - Apple Support