Ok, I will help you out here, because you have been having a tough week.
If you played baseball at a level higher than a 12-year-old or (13 maybe), you would have faced pitchers who were working on their "secondary" pitches (curveballs, sliders or HOPEFULLY changeups). Now hitting is hard, but if you know what is coming, it makes it a little easier, so pitchers work on not tipping pitches.
The best way not to tip pitches is to have the ball/pitches (fastball, changeup, curve, etc.) come out of the same arm angle and release point in the pitcher's windup, so they look like the same pitch until the ball gets close to the plate. Not have your fastball be thrown "over the top" and your curveball thrown sidearm.
Now, MLB pitchers have a lot of movement on their pitches. Their pitches don't always go in a straight line (even fastballs), and many of them have crazy break (left to right, right to left, and up and down) to them, making them harder to hit (and catch). Plus they throw in the high 90s so......
MLB catchers have caught their pitchers before, or have caught enough pitchers to know what certain pitches do. So they are judging in real time where the ball will end up by seeing where the ball is first released and knowing what pitch is coming. And even then, we have seen balls go off the side of catchers' mitts for passballs.
Now, do that while not knowing what pitch is coming or thinking it is a curveball instead of a fastball or vice versa. Good luck.