If you don’t want them to access anything other than the front end, then set your default authorization level to ‘subscriber’ for new members in your dashboard. (The default setting). You can always then go in and select only the specific members you want to write posts etc.
If they don’t need to access the wp-admin area, just don’t set up an account for them. However, it seems like you’re asking if they can access the write new page/post area and not the rest of the admin area. Is that what you’re wanting to know?