Question: I have installed oracle 10g express edition and I did not find the option to 
 create schema..

Is there a option to create schema in oracle 10g express edition
 or else I have to install other oracle 10g..?

To create schema which oracle 10g
 I have to install... what?

Answer: 
You don't need to explicitly create schema, Oracle automatically creates a schema when you create a user (see **[`CREATE USER`](http://download.oracle.com/docs/cd/B13789_01/server.101/b10759/statements_8003.htm#i2065278)** documentation). 

If you really want, you can use [**`CREATE SCHEMA`**](http://download.oracle.com/docs/cd/B13789_01/server.101/b10759/statements_6013.htm) statement and issue it through Oracle Express web interface or from SQL prompt.
As zendar said, creating a user automatically creates their schema (in Oracle these are pretty much the same concept).

When you create a Workspace in apex, it will ask you if you want to use an existing schema or create a new one - so that's another easy option you could use.