The goblet squat is a teaching progression for the squat.
Holding a DB or KB against the chest, arch the back hard, particularly the upper back and take a deep breath in. Engage everything in your core and keep it tight. Set your feet between hip and shoulder width with your toes slightly turned out. Keeping your chest up and everything engaged break at the hip and knee together and descend into the bottom of the squat. Full range of motion for the squat is with your hamstrings completely covering your calves, feet flat on the floor, whilst maintaining the arch in your low back. If full range of motion cannot be achieved then you need to work on mobility. Upon reaching the bottom of a squat drive up aggressively with the legs ensuring you are keeping the chest up throughout with the weight towards the rear of the foot.
The goblet squat is used as a teaching progression for the squat. Due to the load being in front of the body it is easier to maintain an upright torso position and get a little deeper into the squat. Due to the weight being held with the arms the limiting factor will be what you are able to hold onto and not leg strength but like I said it is used as a teaching progression to develop good squat technique before progressing onto more advanced movements.
The goblet squat works better at slightly higher rep ranges (8-20). This allows for good practice of the movement whilst keeping the weight light enough so that the upper body isn’t too much of a limiting factor.