The RTP analysis function takes the selected RTP stream (and the reverse stream, if possible) and generates a list of statistics on it.
Starting with basic data as packet number and sequence number, further statistics are created based on arrival time, delay, jitter, packet size, etc.
Besides the per packet statistics, the lower pane shows the overall statistics, with minimums and maximums for delta, jitter and clock skew. Also an indication of lost packets is included.
The RTP Stream Analysis window further provides the option to save the RTP payload (as raw data or, if in a PCM encoding, in an Audio file). Other options a to export and plot various statistics on the RTP streams.
More details can be found on the https://wiki.wireshark.org/VoIP_calls page.