When you first download Bloc your settings will be set to public. This means that if you upload a Bite without changing your settings, everyone who follows you will see your Bites. Your Bites will also be added to the For You section of the app, so everyone on the app could potentially see your Bite.
You can set your profile to private, which means people need to request to follow you. If you accept them, they will be able to see your Bites in their newsfeed.