5 lat temu
It can be tricky to tell what is spam and what isn't, but as Visty summed it up, if a comment contributes to nothing, it is usually safe to consider it spam, even if the message is not something bad. For instance, comments which are copy pasted from other comments, or comments which just have one or two words or a smiley face.
Do no forget that you should also report inappropriate comments. Those are not spam, but they are reported in the exact same way. They are usually rude and/or edgy messages. If a message is unnecessarily insulting or agressive, it is inappropriate. Do be careful however, swearing is not forbidden on gamehag, and is not inappropriate in itself. Being negative and insulting towards gamehag or its community or something of the like is inappropriate however.
As for what happens when you report a comment: your comment will be judged manually by a staff member. They will check the comment's context and judge for themselves if it is spam or not. If they judge it as spam, you will get 1 SG for reporting it. If it isn't judged as spam, nothing happens. If, however, someone was to abuse the report system and report comments repeatedly even though they aren't, said someone would be banned from the reporting system. All of this information can be found here: https://gamehag.com/forum/t/58039-penalitiesxp-taken-away-bans-and-more