i think it should only pop up once for each player (usually after having created a new account and logging in for the first time)
here an example of an existing pop-up
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i mean something like this, ofc with other content
what i have in mind is something like some screenshots on stuff like how to chat, how to open private chat, links to the chatrules, then ofc how to host a ''normal'' game, a game with mods, how to sign up for a tourney, link to the tech support section in the forums and some basic stuff like this
then i would add it to the toolbar, so you're able to open it up later
the reason i suggest it is, i've already seen at least 10 people who ask how to host a game or open up private chat, also such a pop-up gives a feeling of comfort to new players, they can easily look such stuff up themselves