How to enable autoextend on tablespaces and datafiles

-- Create tablespace with a datafile that will be auto extended to 10Gb
create tablespace TABLESPACE_NAME datafile '/path/to/datafile.dbf' size 2000M AUTOEXTEND ON
MAXSIZE 10000M extent management local uniform size 5M segment space management auto;

If you want to enable autoextend on a smallfile tablespace (if you are trying to alter
tablespace to enable autoextend and getting ORA-32773: operation not supported for smallfile
tablespace) you will have to alter each file individually i.e.:

alter database datafile '/path/to/datafile.dbf' AUTOEXTEND ON MAXSIZE 10000M;