This double bar graph give two types of information.
The striped orange bars show the number of households enumerated in 1999 by number of members, from one (one-person households) to nine or more for the largest households. "Institutional" households (retirement homes, worker or student hostels, etc.) are excluded.
These 23.8 million households count 57.2 million individuals, represented on the bar graph by solid blue bars.

Almost 7.4 million households count only one person, which means that 7.4 million people live alone, so the two bars are the same height. A similar number of households comprise two people, making a total of 14.8 million people in two-person households, and so on. The larger the household size, the larger the difference between the number of households and the number of individuals concerned.
Hence, more than six households in ten (62%) are "small", with only one or two members, though the members of these small households form only a minority of the population (39%).
Conversely, only 200,000 households (0.9% of the total) have seven or more members, though 1.6 million people (2.7% of the population) live in a household of seven or more.

Sources

The data for this graph are taken from the "Households - Families - Total population" volume of the 1999 census report for metropolitan France published by INSEE. They are available on the INSEE and INED websites.
http://www.ined.fr/fr/pop_chiffres/france/familles_menages/menages_nombre_personnes/
http://www.insee.fr/fr/recensement/nouv_recens/resultats/repartition/chiffres_cles/national/france-metropolitaine.pdf