How can I find threats/attacks from a PCAP - Wireshark, Snort [on hold]

I have a pcap file and I am trying to analyze it using Snort and Wireshark.

When I tried the command, which I had showed below, in Ubuntu I was provided with various output such as the date, time, source host, destination host, protocol and there are some others like TTL, TOS, ID, IpLen, DgmLen, Ack, Seq.

Snort -r myfile.pcap

My question is: What do each of these fields mean, and what threats or attacks can be performed with those fields?

TTL, TOS, ID, IpLen, DgmLen, Ack, Seq

I'm attaching a part of the Snort output of the pcap file.

Do I have to write a Snort rule in order to detect attacks? Any help would be appreciated.