Hi @daydreamer9 Welcome to Steemit! The achievement program helps you to understand about steem ecosystem at your own pace and get rewards while doing so.
I would recommend you to complete at least Achievement 1 first or until finish is better details here https://steemit.com/hive-172186/@cryptokannon/achievement-tasks-resources-and-materials-newcomers-retention what to post: beside thediarygame there are 7 other themes you can write about details here https://steemit.com/the1000daysofsteem/@steemitblog/1000-days-of-steem-a-better-life-with-steem-new-content-and-curation-project and this is good article on how to engage/commenting on other post https://steemit.com/hive-133716/@steem-sri.lanka/commenting-is-an-art-tips-to-be-a-good-commenter

I have answered your questions on discord too with this.