Lemmy is still in development and can be a bit quirky. This is a collection of little things I've bumped into which may help you avoid some confusion.
Browsing posts
'Local' only shows you posts from the Lemmy instance you are currently on (e.g. lemdit.com).
'All' will also include posts federated from other instances, and is typically the one you want.
Sometimes 'All' can be selected but only local posts will be displayed. If this happens, toggling between 'Local' and 'All' will fix it:
Finding content on a small instance
Your Lemmy instance will only show posts from communities on other instances if at least one user from your instance has subscribed to those communities.
If a community that interests you is missing, simply search for it and subscribe. You (along with everyone else on your instance) will now see posts from that community under 'All'.
Note: The same is true in reverse! Users on other instances will only see posts from communities on your instance if at least one user from their instance has subscribed to that community.
Searching for communities
Clicking on 'Communities' will display all communities that are either Local to your instance, or that users from your instance have subscribed to
The best way to discover new communities is actually through a 3rd party tool: https://browse.feddit.de/
If you find a community that you are interested in and want to subscribe, search for its URL on your home instance:
Note: Sometimes it takes 10-20 seconds for Lemmy to fetch the actual instance in its search results! Just wait a bit, even if it says there are no results found.
Once you have opened the community through your own instance, you can then subscribe:
"I only see old posts"
The way Lemmy displays "Active" and "Hot" posts at the moment is a bit broken and you may notice the list doesn't change very often. While this is being worked on, you can try sorting by 'New' or 'New Comments':
There is a partial workaround that instance admins can use to get around this, which involves restarting the Lemmy server at regular intervals. lemdit.com automatically does this once a day.
Creating new posts or comments getting stuck on the dreaded "spinning wheel"
This one's a bit elusive, but when it does happen it could be one of two things:
The instance you're on is simply a bit busy and the request fails for some reason
Selecting a language for the post sometimes seems to help:
Finding past private messages, replies, posts, etc.
Clicking on the little bell icon on the top-right will open your inbox:
By default you will only see "Unread" messages, which is a bit counter intuitive. Switching the toggle to 'All' will display all messages:
Closing notes
I hope you found this information useful. Please let me know if there's anything I've missed that should be included, I will expand on this list as we discover new things.