Rebuilding indexes is done using the following statement
ALTER INDEX All ON tableName REBUILD;
This drops the index and recreates it, removing fragementation, reclaims disk space and reorders index pages.
One can also reorganize an index using
ALTER INDEX All ON tableName REORGANIZE;
which will use minimal system resources and defragments the leaf level of clustered and nonclustered indexes on tables and views by physically reordering the leaf-level pages to match the logical, left to right, order of the leaf nodes