Diversity refers to the situation in which a society or a company or other group of people is made up of people who are different from one another. These people could, for example, be from different ethnic groups, different age groups, or different genders.
Inclusion refers to practices which allow these people to all coexist in a way that tends to bring them together rather than pushing them apart. Inclusion occurs when a group of people develops practices and norms that make all members of the group feel welcome. In these groups, the various kinds of people stop feeling separate by virtue of their differences and instead feel connected as members of this particular group.