Questions & Answers about Otworzę okno w pokoju.
If -ę is a present-tense ending for "I", why does otworzę mean "I will open"?
You have learned that endings like -ę usually mean the present tense. However, otworzyć is a perfective verb, which means it focuses on a completed action. When you put a present-tense ending on a perfective verb stem, it automatically creates the future tense! So otworzę means "I will open it and finish opening it."
Why isn't there a word for "I" (ja) in this sentence?
In Polish, the verb ending tells you exactly who is doing the action. Because the -ę on the end of otworzę already means "I", adding ja is completely unnecessary unless you want to add strong emphasis, like saying "I will open it (not you)."
The window is the object being opened, so why does okno stay in its dictionary form?
It is actually in the accusative case because it is the direct object of the verb. However, because okno is a neuter noun, its accusative form looks exactly the same as its basic dictionary form.
Why does the word for room change from pokój to pokoju, and why did the ó disappear?