This is the 288th most frequent Finnish word.
toinen
"Toinen" means "second" or "another" in English.
Here, 'toista' (a form of 'toinen') is used to indicate an alternative or another option, describing 'coat'.
Haluaisin kokeilla sitä toista takkia.
I would like to try on the other coat.
In this context, 'toisen' (a form of 'toinen') indicates an additional item, in this case, 'book'.
Hän osti toisen kirjan minulle.
He bought another book for me.
Here, 'Toinen' is used to denote ordinal number, specifically 'second', describing 'kerta' (time).