There are lots of ways to emphasize adjectives in Swedish. Many of these ways are very similar to how we emphasize adjectives in English.
One way to emphasize adjectives in Swedish is to use så or sådan. Both create the same emphasis, but they are used in different ways. The difference between så and sådan is similar to that between vad and vilken in exclamations.
So, what does så actually mean? Luckily enough, it’s identical in most cases to the English “so”. Så is used to strengthen adjectives like this:
Filip var så glad igår! – Filip was so happy yesterday!
Katjas bil är så stor! – Katja’s car is so big!
Sådan is also used to strengthen adjectives, but only when they are used with a noun directly following them (i.e. only when they are within a noun phrase). For example:
Filip är en sådan glad människa! – Filip is such a happy person!
Katja har en sådan stor bil! – Katja has such a big car!
So, you could say that sådan is the basic equivalent to the English “such”. Notice the different word order, though: In English, we say “such a”, whereas, in Swedish, we say en sådan (lit. “a such”). The basic formula is: [article] [sådan] [adjective] [noun]. Remember this!
Sådan is declined (“conjugated” or “changed”) just like the adjective following it, based on the gender and number of the noun:
en sådan_ snäll_ hund – such a nice dog (common gender)
ett sådant långt bord – such a long table (neuter gender)
sådana snälla hundar – such nice dogs (plural)
sådana långa bord – such long tables (plural)
Sådan can also be used with uncountable nouns (such as mjölk “milk” and mjöl “flour”). In speech, sådan, sådant and sådana are pronounced sånn, sånt and sånna, respectively.
So, you can see that the difference between så and sådan is basically the same as the difference between “so” and “such” in English. Easiest for English speakers would be sticking to this clear difference. In real speech, though, sådan is often substituted by så:
Filip är en så glad människa! – Filip is such a happy person!
Katja har en så stor bil! – Katja has such a big car!
Keep in mind, though, that så is never substituted by sådan! (i.e., It’s never the other way around!)
One last note about så: it is very commonly used with adjectives in everyday expressions such as Ha det så bra! and Ha så kul!. Here, there is no direct equivalent in English – it’s just a Swedish thing.