Search is the one thing Lemmy needs to focus on right away, current search sucks and will run off lots of Reddit refugees their first day.
As of right now, a user in your instance has to search and/or sub to a community from another instance before it gets indexed. You could make some dummy account and sub to hundreds of remote communities so they're locally indexed without having to sub to them on your main account, but that's pretty time consuming and still not a great solution.