You should NOT attach the legs to the servos before the first-time calibration.
When the servos are powered off, their output shafts can be rotated to random angles. If you attach the legs, the robot won't know where the legs are pointing. When the robot is powered, the legs could run into each other or collide with the body. The servos may be damaged after getting stuck for a long time.
The joints of the robot have to be calibrated before future use. Make sure all the servos are connected to the right spot on the circuit board in the right direction, the battery is powering (the yellow LED in the cat's logo is lighting up), and all the legs and head/tail are NOT attached to the servos so that the servos can rotate freely.
Our calibration routine will send a calibration signal to the main board and rotate all the joints to known positions. Then you can attach the legs close to the reference posture, and fine-tune the angles using the software.