to remove data you must either
1) delete from a table (which makes space available for resuse but only to the table and only in the same way as it was originally used (hence index space stays index space and table space stays table space)
2) you truncate the table in which case the high water mark for the table is reset back to its starting level and all space reclaimed is made available back to the tablespace for any use.
If you want to reclaim file space for files assigned to a tablespace you must
1) drop all objects in the tablespace
2) drop the tablespace
3) manually remove files that were assigned to the tablespace
because of #3, you should dump from dba_data_files, the names of files allocated to the tablespace before you drop the tablespace.
I believe that in 11g (maybe 10gr2) individual files can be recovered rather than an entire tablespace. If I am recalling correctly,then the procedure is documented in the relevant manuals. You will have to do some reading.
Good luck, Kevin