FACT: Election Laws
Here's the short explanation.
A filibuster is a Senate rule which effectively allows the minority party in the Senate to require a super majority of 60 votes to pass legislation instead of a simple majority of 51 votes. Since the senate is typically split very closely between the two parties, it forces each party to convince at least a handful of Senators from the opposing party to vote for their legislation, or it will not pass.
Without the filibuster rule, whichever party controlled the senate could completely control everything happening in the senate without opposition from the minority party.
Here's a technical explanation of the filibuster. It's an interesting "parliamentary" feature of our democracy dating back to 1917.
https://www.brennancenter.org/our-work/research-reports/filibuster-explained