If you are going to use the software only for self-educational purposes, it is okay to download and install almost any Oracle software (including SOA suite, any version of the database and JDeveloper).
This is from the Oracle’s Software Downloads page:
“All software downloads are free, and each comes with a Development License that allows you to use full versions of the products at no charge while developing and prototyping your applications (or for strictly self-educational purposes). In some cases, certain downloads (such as Beta releases) have licenses with slightly different terms. You can buy products with full-use licenses at any time from the online Store or from your sales representative.”
Additionally, there is a free version of the Oracle Database (Express Edition, XE), which you can use even for production environments, and JDeveloper is also free to use with the exception of the Oracle WebLogic Server.