Those who commented recently on other people's photos will have been dismayed to find that their comments were not being displayed. HOWEVER it looks as if this has now been sorted - if you scroll down the Latest Activity Feed on the Home page, you will see lots of photos together with attached comments that are now being displayed.
To add a post - click on +Add new Post at top right (if it is not there, you are not signed in - see link at top of page); fill in the details, then click on black button below.
To later edit it, click on the post header to display it, then on +Edit at top right.
If you wish to give somebody your contact details, you may prefer to do so by personal message (click on little envelope at top of page, then on +Compose) rather than putting it in a post which is visible to everyone.