Starting at the top of the TCP header, we can see the Transmission Control Protocol, followed by a summary of what the header represents, as shown in the following screenshot:

Below the summary is the TCP header fields. Whenever there is additional information, you will see an arrow on the right-hand side of the field, which you can expand to see the details.

When looking at the TCP header contents, any information in brackets is generated by Wireshark to help you better understand the details of the header, such as [SEQ/ACK analysis] and [Timestamps], as shown near the bottom of the preceding screenshot.

Let's step through the header fields, starting with the ports.