You might want people to read some of what you write without wanting the internet to read your diary.
That is a reasonable distinction. A private journal can contain unfinished feelings, identifiable details about other people, and thoughts written mainly to get through a moment. A public page needs a deliberate selection.
Ask what you want this piece to do
Do you want someone to understand an experience? See your sense of humor? Know why you care about a subject? Have something to discuss with you?
The purpose can help you decide what belongs. A paragraph about missing the routines of home may represent you well. A real-time account of a family argument may expose more than you intended, especially about people who haven't agreed to appear in it.
You can share the idea without publishing every detail that produced it.
Read it as someone outside the situation
Does the writing make sense without private context? Could another person identify someone from the combination of details? Are you stating an interpretation as though it were a verified fact about someone else's motives?
For an emotionally charged piece, consider waiting before publishing. You may still want to share it later. Time can help you decide which parts communicate your experience and which parts belong in a private place.
Also imagine the audience changing. A link sent to one friend can be forwarded. A public page can be copied. Removing something later cannot reliably retrieve every copy someone made.
Choose a few representative pieces
You don't have to demonstrate total openness. Select writing you would be comfortable standing beside when someone asks about it.
That might include a belief you are questioning, a small experience you keep remembering, or a joke that sounds like you. Leave out anything you feel compelled to explain only because you fear being misunderstood by a particular person.
A public page can develop slowly. Adding one piece you like is enough for today.
Know which part of the product is public
On Sinapsis, the Thoughts Portfolio is a public page made from thoughts you select. You choose whether to create it and share its link. Keep writing that must remain private in a private journal rather than assuming an anonymous social post is private.
Anonymity, privacy, and public sharing describe different things. Before posting, understand where the thought can appear. Before adding it to your Portfolio, consider whether you want it to become part of a page you share as yours.
Try selecting one piece with a clear purpose and reviewing it for context and identifying details. You can let someone see more of how you think while keeping much of your life to yourself.