Learn Polish: Kino jest po prawej stronie. - The cinema is on the right.

Stronie is a form of the word strona, which means side. In Polish, you literally say on the right side (po prawej stronie), whereas in English it is common to just say on the right.

Why do the words prawa and strona change to prawej stronie?

They are in the Locative case. The preposition po requires this case when talking about being located on a specific side. For feminine nouns like strona, the ending changes to -ie, and the feminine adjective prawa changes to prawej.

I thought the word po meant after. Why does it mean on here?

While po often means after (like in po pracy, meaning after work), it is also used to indicate location along a surface or side. In fixed directional phrases, po translates to on, as in po prawej stronie (on the right) or po lewej stronie (on the left).

Why doesn't the word kino change its ending?

Because it is the subject of the sentence, so it stays in the Nominative case, which is its basic dictionary form. Neuter nouns ending in -o like kino just use this standard form when they are the main focus of the sentence.