Deals, organizations, and people all have default fields such as name and various contact details set up by Pipedrive, but you can also add new custom fields. For example, you could add ‘Job Title’ as a custom field under contacts and later filter out contacts based on a certain job title.
To customize fields for people, organizations and deals, go to Settings > Customize Fields to add and edit them.
You can also mark a specific custom field to be always visible on sidebar (in the detail views) and when adding data to ensure all the necessary info is always there. Different formats (addresses, phone numbers etc) are available.