Due to the way the Fediverse currently works, if you publish a post while you still have zero followers, that post will probably not be visible to anyone except people on your server. When people follow you, they will see your posts from that moment onwards, but there’s generally no backfilling to show them your previous posts.
On Mastodon, you can make everyone see past posts by pinning them to your profile. Pinned posts are backfilled and will become visible to anyone who follows you. You can pin up to five posts at once, and they will all be backfilled. Unpinned posts will not be backfilled though.
In general it’s a good idea to wait until you have at least some followers from other servers before you publish your most interesting stuff. Even a handful of followers will give your posts much more visibility across the Fediverse, as you only need one follower from a server to make your posts visible to that entire server.