Btw is it alright to advertise stuff here? Like websites that sell games or stuff?
Basically, something like "I play game x with this particular mod: {link to mod's website}" is absolutely fine.
But if you are posting a link which you get paid to post as many times as possible, or one which you earn a commission on for every click, then that isn't so cool. That's called spam, and if we let one person do it, then everyone would do it, and the entire forum would be clogged up with adverts.
Basically, we will always give you the benefit of the doubt - we can see you are a genuine user, and not a robot or anything, so we aren't going to get you into trouble over a single link, only if you started posting the same link 100x or something crazy like that
The line's pretty common sense TBH, if you are posting a link to be genuinely helpful to future readers, that's fine. If you're posting it 100 times or as part of some slightly underhand business, that's too far.
But, please, don't worry or be concerned about this. We can see you are a genuine user trying to help others, so that's absolutely fine. There is absolutely no need to constantly worry about a mis-step, seriously, you'll be fine :)
And if you have any further questions, please click on my name, select Private Message, and ask me there :)
Richard