When you first create a Guide it will be in "draft mode" where only you, administrators of the Space you created the Guide in, and people you invite to the Guide can access it.

While in draft mode, the Guide will have the label "draft" on the card, and you will see a message on the right side of the Guide with a "Publish Guide" button:

You will need to publish the Guide for it to be visible to other members. Once published it will be accessible to anyone who has access to the space.