After sending the header, the content portion is sent, if expected. Content can be sent both in requests and responses. Both static content, where the size is known, and dynamic content, whose size is not known at the beginning of transmission, can be sent. This is controlled by the Content-Length and Transfer-Encoding header fields. These fields are typically managed by the HTTP client used.
The actual content is then sent in binary form. The actual encoding and decoding should be properly defined using the Content-Type header field and might have to be performed by the application itself. If using the Waher.Content NuGet library,with additions, encoding and decoding can be done for you.