Integer
This is a numerical field for non-decimalised data, e.g. 'Number of Employees'. As a numerical field you will be able to query things such as 'less than', 'greater than', 'between'. 
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​Note: The largest integer value we can accept is 2,147,483,647 - anything higher than this would need to be stored as a 'text' data type.

Float
This is a numerical field for decimalised data e.g. monetary values such as 'Total Spent'. As a numerical field you will be able to query things such as 'less than', 'greater than', 'between'. 

DateTime
This field will store data in the format dd/mm/yyyy hh:mm:ss and can be used for things such as appointment bookings in order to trigger pre-arrival communications. 

Date
This field will just store a date in the format of dd/mm/yyyy - you can use this for things such as renewal dates of services, in order to trigger annual notifications. 

Time
This field will store a single time in the format of hh:mm:ss against a contact. When querying, you have the same options as searching on numerical data but you must search on the values in 24hr format, without decimalising.

Boolean
This field allows you to store true/false data against a contact, which you would then query using yes/no. 

Text
This is a straight-forward text field, with up to 4000 characters, allowing you to store whatever custom data you like without needing a specific format like the above. 

EmailAddress
This field allows you to store a secondary email address against a contact, but wouldn't be the field used to send communications to. The existing 'Email Address' field will be the primary field used for this purpose. 

PhoneNumber
This field allows you to store additional phone numbers against a contact but, as above, the field used to send SMS would be the existing field and not any additional custom fields you may create.