You have a few options available. The easy one:
CREATE TABLE your_table (field_a CHAR(1), ... ) TABLESPACE your_tablespace;
This will create the table "your_table" in the "your_tablespace" tablespace.
You could also create a user to make him use your tablespace as a default tablespace, thus all his objects (not only tables!) would be created in that tablespace:
CREATE USER your_user
IDENTIFIED BY "your_password"
DEFAULT TABLESPACE your_tablespace
TEMPORARY TABLESPACE temp;
GRANT CONNECT to your_user;
You could also modify an existing user to change the default tablespace:
ALTER USER your_user DEFAULT TABLESPACE your_tablespace;
From that moment on, all NEW objects will be created in your_tablesapce (Previously existing objects will NOT be moved automatically!)
To move a table from one tablespace to another:
ALTER TABLE your_table MOVE TABLESPACE your_tablespace;
Think that's all...