I need a Schengen visa to visit Portugal as a tourist. When trying to make an appointment on vfs website I got confused:
Which one should I select as the category?
The first three options clearly are not right for you.
The remaining two look more likely. I think you should select the Short Stay - Schengen Visa.
While the Tourist Visa at first glance looks more specific to you, it might be a special national visa category reserved for package deals etc. with specific conditions. You already say you need a Schengen visa, and the option is the only one that clearly says it is one.
In principle, Schengen short stay visas don't distinguish between categories of purpose like e.g. the US does (with B1 for business, B2 for tourism, and a combined B1/B2 for both).
In most cases, you'll need to stick to the purpose you give at the visa application when you first use your visa for entry. The consulate will decide if you are issued a single, double, or multiple entry visa, and if you get a multiple entry visa, you can use it again for a different purpose another time without applying for a new visa.