Are you using the correct default post visibility? If it's on the wrong setting, you may end up accidentally just posting to yourself.

1. Log in through your server's website
2. Go to ⚙️ Preferences > Other (if you're on mobile click ☰ to find Other)
3. In Posting Defaults section choose your default privacy
4. Click Save Changes button at top

Whatever default you choose, you can manually change a post by clicking its visibility icon.

More info about post visibility: https://fedi.tips/how-to-use-mastodon-and-the-fediverse-basic-tips/#WhoCanSeeMyPosts