The Leads Inbox lists your pre-deal contacts - people with no open deal yet - ranked by lead score. It is where you triage new interest and decide who to work first.
Open Sales and choose Leads Inbox.

Each lead shows its company, score and status. Use the All / Hot / Warm / Cold filter in the top right to focus on the leads most likely to convert. Triage the hottest first.

Click Open on any row to see the full contact, their activity and score breakdown, and to move them into your pipeline when they are ready to become a deal.