It's not clear to me exactly what you are asking so I will give a broad set of answers.
All field names are based on their display titles, not the Internal Name.
If you only want the value of specific fields to be returned you use
$select=followed by the field names. The following example will return only the values of the fields I specify in the query string and the item's
__metadatawhich is always returned with a query.
3. Complex fields such as lookups (including users whose values are lookups to items in the
UserInformationList) need to be specified in the query string using
$expand= For example if I am looking at a task list with a field called "Assigned to" I would specify my URL as follows:
This would give me a full object graph of the CreatedBy (internal name
AssignedTo fields. Fields that are shown in dropdowns or radio/check boxes in the standard SP UI generally have their values encoded in their object's
Value field. Using the example of a task list again I would look for the item's priority in the
PriorityValue field or if I chose to expand the object it would be in