Short answer
HubSpot's KB: to sync LinkedIn leads you need to be a Super admin, Content Admin or Lead Gen Forms Manager on the LinkedIn Business Page. Make Email a required field so HubSpot can create contacts. For Facebook and LinkedIn you can pick a sync timeframe. Once synced, use the leads in workflows like any form source.
1. Ads settings
Ads settings in my demo portal.

2. Facebook
See Facebook lead ads.