You only see posts from people you follow, you can just unfollow (or mute/block) whoever you don't like to see on your timeline. If you're scrolling the trending/explore page then maybe you should try switching servers or just stick to the home feed which has toots only from the accounts you follow.
Personally, I initially started with following accounts of some companies or softwares that I use or am passionate about like The Fedora Project, The Tor Project, Bitwarden, Blender, Proton, some game engines (and their creators) etc. You can usually find their mastodon handles on their website and/or somewhere on their twitter profiles.
After that I branched out from there gradually, following people as I found them in discussions, the explore page and through some 3rd party discovery tools as well like "Followgraph for Mastodon" which looks up all the people you follow on Mastodon and then the people they follow then it sorts them by the number of mutuals.
Figure out what sort of thing you'd like to see, check out the related hashtag feeds. You can follow tags as a good way to get started and follow individual people as and when they pop up with something cool.
Yep, a large portion of the content is exactly that. Mastodon is successfully replicating the Twitter experience.
I'm not a huge fan of the format either.