As noted above: there’s no promotion / relegation in U.S. pro sports, and all of the major professional team sports in the U.S. have both (a) a system of playoffs to determine a season’s champion, and (b) are organized into subgroups of conferences and divisions, which are what determine which teams make the playoffs.
For instance, in the NFL, a team is either in the American Football Conference (AFC), or the National football Conference (NFC). Twelve teams make the playoffs each year – six from each conference.
Within a conference, there are then four divisions (North, South, East, and West). The team with the best record in its division at the end of the regular season makes the playoffs (so, that’s four from each conference). Then, there are two “wild card” teams in each conference, which also get into the playoffs – the wild card teams are the two teams in a conference with the best record, who did not win their division.
Having the best record in your conference means (i.e., the “#1 seed”) that you’ll be playing at home through the playoffs, and it also means that you’ll get a “bye” (a week off) during the first week of the playoffs. (The #2 seed also gets that bye.)
Then, the two conference champions (as determined by three rounds of playoff games) meet in the Super Bowl, which is played at a neutral site. The winner of the Super Bowl is the league’s champion for that season.
A team’s overall record / standing in the league for the season doesn’t factor into any of that. Having “the best record in the league” for a season is a minor point of bragging rights, but there’s no award or trophy associated with that, and there have been a whole lot of teams who went into the playoffs having had the best regular-season record, only to fall short of winning the championship.
You’ll very frequently hear mention of a team’s position within their division, as that’s a relevant point (winning your division ensures a playoff spot). When you look at the league’s standings online, it’s always divided up by conference and division.
About the only thing that overall league standing in the NFL acts to determine is the order in which teams will draft new players (coming out of college) before the next season, as well as the order in which teams are allowed to claim players off of waivers when they’ve been released by other teams. In both of those cases, the “reverse order” is used (i.e., the team with the worst record gets the #1 draft choice).