"The cat is walking on the bed."
Translation:Kot chodzi po łóżku.
Actually, it's more complicated. This "po" and that "po" used with names of languages are completly different.
You can use "na" when the cat is on the bed and then you say: "Kot jest na łóżku" (na + locative). The cat is on the bed.
You can also use "na" when the cat is not on the bed yet but then the cat jumped onto the bed. "Kot wskoczył na łóżko" (na + accusative)
And eventually, the cat is on the bed and is walking around on its surface - "Kot chodzi po łóżku" (po + locative)