Unlike personal pronouns, there are quite a lot of impersonal pronouns in Lithuanian. Some may almost seem like synonyms (toks and šitoks; tas and šitas).

These are the main impersonal pronouns, with which you can start learning:

tas, ta - that
toks, tokia - so; such; suchlike
kuris, kuri - which, who
pats, pati - own; self

The declension of these pronouns:

Other impersonal pronouns

šitas, šita - this (declined as tas, ta)
šitoks, šitokia - so; such; suchlike (declined as toks, tokia)
šis, ši - this (declined as kuris, kuri)
kas - what, who (declined as tas; only masculine singular)
keli, kelios and keleri, kelerios - how many; several; few (declined as numbers 4-9)
kelintas, kelinta - 'which one out of some' (declined as first declension adjectives)
koks, kokia - what (declined as toks, tokia)
manas, mana; tavas, tava; savas, sava - are most likely to be changed by possesive pronouns (declined as first declension adjectives).
joks, jokia - none; any; whatsoever (declined as toks, tokia)
kitoks, kitokia - different; otherwise (declined as toks, tokia)
kiekvienas, kiekviena - every (declined as first declension adjectives)
kitas, kita - other (declined as first declension adjectives)
visas, visa - whole (declined as first declension adjectives)
niekas - nothing (declined as first declension adjectives)
viskas - everything, all (declined as first declension adjectives)