You can access technical guides within the documentation tab of the specific RFA API (Java, C++, .NET) you are interested in. Refer to the API page to choose your specific language.
That being said, as @Gurpreet. stated, if you are planning on new development, please refer to the link provided above. EMA is our strategic API and will continue with new features and enhancements. RFA is supported but is in maintenance mode only.
Please see Why Migrate from RFA to EMA API? video. From this Video, you will learn how migrating from RFA to EMA can simplify access to the data that you require; the benefits of EMA; and where you can find the resources to help you migrate etc.