If it's set to PUBLIC (default for all non-Pro accounts), then your initial post will be visible on the Community Firehose.

BOOSTS and REPLIES will only be visible to those who follow you from within their MY FRIENDS column.

Pro accounts have even greater control over post visibility, with the ability to choose between PUBLIC, UNLISTED, FOLLOWER ONLY, and DIRECT MESSAGE options.

Pro accounts can also create EXPLODING POSTS, which "detonate" after a selected interval. #CoSoTips