If your site makes its money selling ads that is most likely only of interest only to the tax authorities where your company is located. It doesn't matter where your site users are located. You advertising income will just be another entry on normal business income taxes.

If your site makes its money selling subscriptions, that money is business income on your normal business income taxes but also likely will be subject to sales taxes in the places where your subscribers are located.

If you have customers in the EU, you'll need to collect and file quarterly VAT there (the EU has its act together so you only have to register in one country, and file a quarterly report breaking down sales by country, and that one you registered in will deal with distributing the money to the rest).

If you have customers in the UK you will have register separately with them, because the morons implementing Brexit failed to arrange to stay in the unified online VAT system of the EU. (Not that you can currently actually register in the UK. We applied for our VAT registration number something like two years ago and they keep saying that HMRC is very busy and will eventually get to it. In the meantime we are suppose to collect and hold UK VAT, but not supposed to call it VAT).

If you have customers in the US you might have to deal with sales tax in 45 states. Unlike the EU VAT the rates are not uniform within a given state. You have to deal with different rates in each county, possibly each city, and possibly even in different areas within a city--and tax boundaries do not always line up with zip code boundaries so to do it right you have to collect exact address information for your subscribers.