Your Mastodon feed won't improve through passive engagement. There is no algorithm to suggest and share what you liked.
You must actively follow different people to see what they boost, and you must boost for other people to see. Some people are from different servers. You will see more of what they see organically. You can also hashtag to increase visibility.
There is no quote retweet either. You have to actively engage and comment in the thread.
@antimnguyen i'm BRAND NEW here - thanks for this, it's helpful -
do we need to specify usernames fully including their domains? do we only see users on the same domain/server as us?
@fearnot By default in your search bar, typing the username will show matches on your server. But typing the entire username address will find the specific person on the entire network.
You can find posts/boosts from anyone if you follow them. The more you do, the more you will discover regardless of server.
An-Tim Nguyen 
MystMastMarcus