This is the 13966th most frequent Polish word.
postanowiłem
"I decided."
This sentence uses 'postanowiłem' to convey a conclusion made after thoughtful deliberation.
Po długich rozważaniach, postanowiłem zmienić pracę.
After long consideration, I decided to change my job.
Here, 'postanowiłem' indicates a personal decision or determination to undertake an action, in this case - learning to play the piano.
Postanowiłem nauczyć się grać na pianinie.
I decided to learn to play the piano.
In this example, 'postanowiłem' is used to express a resolved intent towards achieving a goal set in the future.