Any Successbook123 user who visits your profile can click on the "Space" tab but what they see on it depends on what privacy your posts are set to.
The visibility of posts on your own Space depends on the audience you choose for each post using the viewer selector. For example, a contact will see posts you've set to Contacts, Contacts of Contacts and Public, while a non-contact will only see posts you've set to Public. If you do not have any public posts, then a non-contact will see a blank Space tab.
To edit how your birthday appears to your contacts, click the "Edit Profile" link at the top of your profile and find the Basic Info section.
Choose which parts of your birthday your contacts see. Use the dropdown under your birthday fields to choose. You can display your full birthday, or just the month and day, or you can hide your birthday completely.
Before you post, you can choose who you share it with by selecting either of two options which include:
This tool is ever present whenever you want to post a Success Story or Message.
To let you know at all times who you shared your post with, a label will accompany your post indicating this. If you wish to change who can view your post later on, use the viewer selector to choose an appropriate option.
It is important to note that the above is only true if you are not posting on someone's profile otherwise these options are only available to its owner.