OData (http://www.odata.org/) is a standardized protocol built over existing HTTP and REST protocols supporting CRUD (Create, Read, Update, Delete) operations for creating and consuming data APIs.
We access an OData service via an URI like https://customerapi.fts-crm360.com/data/Contacts() using HttpMethod GET.
That request will return all the contact entities.
You have to specify Http Headers (X-Crm360Api-Token, X-Crm360Api-CustomerName, X-Crm360Api-DatabaseAlias) to allow the api to return results.
To access a particular entity, you can refer the entity key in the URI to access the particular record like https://customerapi.fts-crm360.com/data/Contacts(132). The contact key here is 132.

The below lines will document the most used and helpful queries when dealing with an OData service:
- $format : By default the data returned is in an XML feed. This query allows you to change the format of data. https://customerapi.fts-crm360.com/data/Contacts()?$format=json
- $top : This query option helps to limit the data returned by the service. https://customerapi.fts-crm360.com/data/contacts()?$top=3
- $skip : This can be treated as the opposite of $top. The skip queries can be used to skip records. https://customerapi.fts-crm360.com/data/Contacts()?$skip=2
- $inlinecount : This will return the total number of records without the filter as part of the response payload. https://customerapi.fts-crm360.com/data/Contacts()?$inlinecount=allpages
- $orderby : Use this to sort the records returned by the service. https://customerapi.fts-crm360.com/data/contacts()?$orderby=FirstName desc
- $expand : Expand related data inline with the results. Say, in case you want to return all the PurchaseGoods along with their PurchaseGoodCategory, use the following URL. https://customerapi.fts-crm360.com/data/PurchaseGoods()?$expand=PurchaseGoodCategory
- $filter : This can be compared to the 'where' query in SQL. Lets say we want to get all the PurchaseGoods with PurchaseGoodCategoryId equals to 3, then use https://customerapi.fts-crm360.com/data/PurchaseGoods()?$filter=PurchaseGoodCategoryId eq 3
- $select : As in any SQL query, this query option can be used to Select specific or all fields of an Entity set or entity. https://customerapi.fts-crm360.com/data/PurchaseGoods()?$select=SKU, LongName

For more documentation on Odata protocol visit http://www.odata.org/.