"se" can stand for "hän" in spoken Finnish. The sentence decides its meaning.
"se" is also an ordinary written word. Check the meaning note beside each example; not every use is a shortening.
Spoken form of 'hän': in speech 'se' covers people too
Se osaa ruotsiakin. - She speaks Swedish too.
se here: she - spoken 'hän'
Written Finnish: Hän osaa ruotsiakin.
Se on mun työkaveri. - He/she is my coworker.
se here: he/she - spoken 'hän': in speech 'se' covers people too
Written Finnish: Hän on minun työkaverini.
Se ei tuu tänään. - He/she isn't coming today.
se here: he/she - spoken 'hän'
Written Finnish: Hän ei tule tänään.
Ei se mitään. - No worries, it's nothing.
se here: it - also used for 'he/she' in spoken Finnish
Se maksaa kolme euroo. - It costs three euros.
se here: it
Written Finnish: Se maksaa kolme euroa.
Se on tuol. - It's over there.
se here: it
Written Finnish: Se on tuolla.
Spoken and written Finnish are different registers. The examples show how "se" is used here and pair it with the written sentence. Learn the meaning in context rather than replacing every occurrence of a word.