Sorting is the manipluation of data to represent it in a specific order based on a set condition (fields or functions are the conditions in either a gorup by or order by clause).
Indexing is creating an object or set of objects which store summary information concerning the data within a table used to reference and lookup the data.
By default a table is not predetermined order (call a heap), however when you create a clustered index it will stort the data based on the conditions of the clustered index (you can only have one clustered index per table).
Hope that is clear enough.