Go to the Oracle website at http://www.oracle.com

Click on Downloads, and then under Database, click on Oracle Database 11g Express Edition.

Accept the Licensce agreement and select the download version you are interested in.
For example, you can download the Oracle Database Express Edition 111g Relase 2 for Windows x64 database.
The OracleXE112_Win64.zip file is downloaded.

Unzip the .zip file by right-clicking on the file and selecting Extract All..., then click Extract on the next window.
You will now see a DISK1 folder, and inside it is the setup.exe executable file.

Double-click on setup.exe to start the Oracle database installation.

On the Welcome to Install Wizard window, click Next.

Accept the terms in the license agreement, and click Next.

Enter a password, and click Next.
This is the password to the SYSTEM account and you can use any password you wish just note it down.

Continue on the next windows, click Install to install the database, and click Finish once installation is complete.

If the completion of the previous step does not automatically take you to the database administrative window in your browser, you can manually open your browser and access the database administrative screen by typing the following URL into your browser: http://localhost:8080.