This is the 768th most frequent Ukrainian word.
ту
"Ту" in Ukrainian means "that" (feminine accusative form) or "there" depending on context.
The word 'ту' refers to a specific concept that has been previously mentioned, acting as a demonstrative modifying the noun 'думку' ('idea').
Ту саму думку висловила й вона.
She also expressed the same idea.
The word 'ту' corresponds to the English word 'that' and is used here as a demonstrative adjective modifying the noun 'книжку' ('book').
Я прочитав ту книжку, яку ти мені дав.
I read that book which you gave me.
The word 'ту' specifies a particular song that contextualizes its importance in the sentence, modifying the noun 'пісню' ('song').