Go to "communities", select "all" and search for the subreddit equivalents you want. Then you can subscribe to them - their posts will be visible when you browse by "subscribed" on the main page. "Subscribed" is basically the equivalent of "Home" on reddit.
Subscribe to the communities you want. I usually do so by visiting one directly, like https://lemmy.world/c/technology. Once there, the sidebar has a button for it.
I’m getting older, so my speed at picking up new tech is a little slower than it used to be, but I’m finding my footings.
From my limited interaction so far, I think what also happens is that there are lot’s of different servers to connect to, and each server can have it’s own “sub-reddit” which are called communities.
For example, lemmy.world might have a “showerthoughts” community, but another server like “sh.itjustworks” can also have a “showerthoughts” community. When you subscribe to a community, you subscribe to that servers instance… so depending on which server community you subscribe to, might not be the most active one. at least that’s how I have pieced it together. Please someone correct me if I am waaaaaaaay off!