If you do not understand the topic, you don't need to reply, you can just read and see the development of the conversation in the thread. If you are confused you can join the discussion by asking questions that have a relation to the topic. And if you wanted to participate, you can also use the search function and do research and give supporting sites that can aid the discussion.
I think people will reply to a topic or respond to another post because they want to add some relevant opinion or want to correct something that went wrong. If the reply contains no such things then I believe it is a spam post whose sole purpose is to increase the activity count. If they don't have any relevant ideas then I don't think they need to reply to the post and the best advice is to read.
In short, learning is the key in order for you to actively participating in every discussion.
The OP doesn't seem to have anything to worry about as some of the advice and guidelines have been mentioned on the previous page. I hope he has a great journey on the forum and no longer feels insecure with his minimal knowledge.