The MLB.com API is quite an illusive thing. This should help you get to some commonly used end points.
This seems to be the newest way to access the API and is suggested by MLB.com.
http://statsapi.mlb.com/api/v1/schedule/games/?sportId=1
http://statsapi.mlb.com/api/v1/schedule/games/?sportId=1&startDate=2019-03-28&endDate=2019-09-29
http://statsapi.mlb.com/api/v1/game/[gameID]/content
http://statsapi.mlb.com/api/v1/venues
http://statsapi.mlb.com/api/v1/venues/[venueID]
http://statsapi.mlb.com/api/v1/teams
http://statsapi.mlb.com/api/v1/teams/[teamID]
This is an older way of accessing the API. There is a message in the JSON data that this URL is deprecated but you can access game and social media data through this directory:
http://gdx.mlb.com/components/game/mlb/
http://gdx.mlb.com/components/game/mlb/year_2019/month_03/day_28/master_scoreboard.json
http://gdx.mlb.com/components/game/mlb/year_2019/month_03/day_28/miniscoreboard.json
http://gdx.mlb.com/components/game/mlb/year_2019/month_03/day_28
In this directory, you'll see the matchups for the day in the URL above. Click into those individual matchups and get more options for game-specific data including, lineups, box scores, plays, event logs, and more.
http://gdx.mlb.com/components/game/mlb/twitter/
Get Atlanta Braves Insider tweets:
http://gdx.mlb.com/components/game/mlb/twitter/atlInsiderTweets.json
http://gdx.mlb.com/components/game/mlb/twitter/teams
Get Atlanta Braves official tweets:
http://gdx.mlb.com/components/game/mlb/twitter/teams/BravesTweets.json
http://gdx.mlb.com/components/game/mlb/twitter/fanCave/
http://gdx.mlb.com/components/game/mlb/twitter/sportsonearth/