Hey welcome. That’s a bit of a complex answer, because you said “cut”.
First, it depends on which machine you have. The performance machines are far more powerful than the craft units (the spark and aura), and how thick you can cut depends on what material you’re working with.
Balsa wood? Probably half an inch or more in a performance model. Aluminum foil? none of the glowforge models can cut metal.
So, let us know what machine you have and what material you’re trying to work with and we can give you some advice! 
In the meantime, I bet you’ll like this FAQ. Particularly look at #6: