You can mute or block accounts that you don't want to see posts from. Click on the ⋯ below a post and select mute or block.
If you see something rule-breaking, you can report post the same way by clicking ⋯ and then report.
You can also filter words and phrases as @diazona suggested: https://fedi.tips/filtering-your-timeline-to-hide-posts-on-mastodon/
By the way, another feature you might want to explore is Lists, which let you make themed mini-timelines: https://fedi.tips/how-to-use-the-lists-feature-on-mastodon/
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