REST endpoint is one way of retrieving data on client side. REST operations are using datasets, which  are treated as entity item collections.

Personally the easiest way of using REST endpoint is to use XrmServiceTooltkit.REST library.

Where to find datasets?

http://servername:port/OrganizationName/XRMServices/2011/OrganizationData.svc/

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Where to find fieldnames used in particular dataset?

http://servername:port/OrganizationName/XRMServices/2011/OrganizationData.svc/entitySet

Request for eg. new_errorSet will return all items created in this entity.

How to filter data?

http://servername:port/OrganizationName/XRMServices/2011/OrganizationData.svc/new_errorSet?top=10&$select=new_name&$filter=new_name eq ‘SystemUserPreCreate()’

More about querrying via REST can be found here:

http://msdn.microsoft.com/en-us/library/gg334767.aspx