How to see tablespace usage for Oracle Database?

Please execute following commands as "sys";

select b.tablespace_name, tbs_size SizeMb, a.free_space FreeMb
 from  (select tablespace_name, round(sum(bytes)/1024/1024 ,2) as  free_space from dba_free_space
 group by tablespace_name) a,
 (select tablespace_name, sum(bytes)/1024/1024 as tbs_size
from dba_data_files
 group by tablespace_name) b
where a.tablespace_name(+)=b.tablespace_name