This is the 15069th most frequent Polish word.
roślinę
"Roślinę" means "a plant" in English.
In this sentence, 'roślinę' is the direct object of the verb 'podlewam' (I water), referring to 'the plant' in a singular and accusative case.
Podlewam roślinę codziennie, aby mogła zdrowo rosnąć.
I water the plant every day to help it grow healthily.
Here, 'rośliną' is the instrumental case, used to express the tool or companion with which something is done, correlating with 'z' (with).
Przyszedłem z rośliną, którą kupiłem w sklepie ogrodniczym.
I came with the plant I bought at the garden shop.
In this example, 'roślinę' is again in the accusative case as the direct object of 'znalazłem' (I found).