Well, most of the time, it works in a very similar fashion to Reddit: voting, communities, etc.
The main difference is that it's federated. As in, there are lots of different instances (servers) that you can join to access Lemmy through. Each server has a different administration and set of rules. Because Lemmy is federated, you can interact with posts, communities, and users from other instances from your instance. You can even host your own instance. If you can't search for a community that you know exists, you might have to search for it like this: !community@instance.name to sync it with your community.
Then you might want to subscribe to some communities you're interested in. Find interesting communities here. I usually scroll with Subscribed/Local/All>New as Hot or Top usually show you posts you've already seen. Local shows you posts on your instance. All shows you posts from all federated instances.
Hope this helps.
EDIT: Here's a list of instances with their different features.