In recent times, Russia has used American social media and other online forums to spread various things. Through spreading falsehoods and propoganda, they are able to turn Americans against each other and create unnecessary controversy and conflict. Instead of focusing on important topics, these conflicts take control and appear to become the most pressing matter of the time, even if they would otherwise seem to be a simple and trivial matter.
One example of something that should be common sense (but for whatever reason, isn't) is that vaccines are miracles of modern technology. However, in recent times, opinions towards vaccines have worsened. This is due to a number of reasons, one being the fact that vaccines have worked so well that most people don't realize how many terrible diseases have been wiped out, hence there being "no more evidence" that they had ever worked at all. One major thing that links these rumors is that a number of them have been traced back to a number of Russian social media accounts run by bots. The purpose of this false information is likely similar to what I said about trying to turn Americans against each other.
Another example of Russia manipulating the United States was during the 2016 Presidential Election. Though there is very little evidence that vote numbers were tampered with directly, there is plenty of evidence that suggests that social media was used to influence the minds of Americans. Using the advertising systems that websites had at the time, Russian "trolls" were able to target specific demographics with what was about as close to the perfect material for creating as much controversy as you could get. This issue persists today, across several different countries.