If you've connected your keyboard but it seems to type the characters that should be on the other half, you've likely connected the right half of the keyboard instead of the left one.
By default, only the left side can be used as the master half. You can change this by setting the handedness.
To use the right or either side as the master, you'll need to set the so-called "handedness". To configure handedness, please read the article Setting Handedness in the official QMK documentation.
Be sure to only use one USB cable when connecting your keyboard to your computer. The TRRS cable in the middle will connect both halves to each other. Connecting both cables may cause damage to the keyboard or worse, and in the event that it won't, one of the halves will be mirrored.