seriously confused

on my packet of white rice it says that there are about 75g of carbohydrates per 100g , then straight underneath it says glycaemic carbohydrates is 55g per 100g ??? whats the difference ?

The 75g is the actual macros. Then what they do is take the glycaemic index of the rice and multiply it with the actual amount to get the glycaemic carbohydrates. In this case 55g per 100g, that means that ingesting 100g of rice has the same effect on insulin as that of 55g glucose.

ok but my muscles still absorb 75g of glycogen?

No. There is fiber in the rice which does not get digested. Then the process whereby carbohydrates are converted into glucose and then to glycogen loses more energy and there are some byproducts. Thereafter the amount going to your muscles depends on how much is available. Vital organs like e.g the brain take priority over muscles. It could also be that your muscles are not very depleted of glycogen stores, in which case the glycogen could be sent elsewhere. The amount of glycogen your muscles will absorb depends on your insulin levels.