Can anybody help me what is the meaning of "Submit flag & press enter"

Off-topic
1

I’m in the

Active seasonal machine > Headless

and when i start the machine it is asking like this.

2

For each machine you play, you have to submit two 32 character codes, called flags. These confirm you got into the machine, first as a normal user, second as admin/root.

If you manage to get inside the machine, there will usually be a user.txt file in the first directory you logged into. Once inside, you can escalate your privileges to root or admin using various methods and you can find root.txt inside the /root directory if you are playing a Linux machine.

You can copy the codes inside these files and submit them to HackTheBox. If you manage to enter both the user and root flags, you beat the machine.