The combined ticket at €31 gives you access to the museum at the time you have chosen for the tour. After the tour, you are free to visit the rest of the museum, if you wish.

With the guided tour- full price €12 the admission ticket for individual visitor is not included.

Guided tour - Reduced price at €9 is for visitors benefiting of a free admission to the museum: under-18s, under-26s living in the European Economic Area, membership card holders (Amis du Louvre, Louvre Mécène, Louvre Professionnels) people with disabilities and people on income support.
Complete liste of tariff conditions on: https://www.louvre.fr/en/visit/hours-admission#visitors-eligible-for-free-admission