The "Previous Company Roles" block allows you to track a person's change in role (job title) at a company and/or a change in their primary company including the dates when these changes took place.

Each time you change a person's job title, or primary linked company, the history is automatically updated with a new entry to record the change. This tab can be found under the "Details" tab on any contact record.

Click the heading to expand this and show the full history.