Is the Oracle database free for private developers, just testing the database, or do I have to personally contact them in order to pay them? I just went to the Oracle download page and downloaded 2 pcs. 1 GB install files, installed the database on my Windows 7 machine and then started using it.
The database software which is available for download over the OTN is under the development license and certainly can be used for learning purpose. I won't suggest to use XE edition if you are willing to work as a DBA because for production shops, its the Enterprise Edition (or SE) which is used everywhere.
Did you pay heed to the license agreement you accepted before downloading the software ? The usage restrictions are spelled out clearly.
The limits for 11g XE are also documented -