I cannot find an event, community or chat
Usually it is in a different tab than you expect.
My own event is not in the list
Events you organise appear under Manage, not Browse. Browse shows events open to you from others.
An event someone mentioned is not there
It probably belongs to a community you have not joined yet. Join the community first and it will appear.
A sub-group or channel is missing
You only see the sub-groups and channels you are a member of. Expand the community in the Communities tab to see what you belong to, and ask an admin to add you to the rest.
I cannot find an old message or file
Use the search box at the top and switch the category to Documents, Photos or Links. Searching by file type is usually faster than scrolling.