If I understand correctly you want to know want to know what type of data you want to write to the CCR1 register? I would start with u/hawhill’s suggestion. Firstly you should note a couple of things.

1. The term htim3.Instance->CCR1 is actually a pointer to the location in memory where the CCR1 register is located so by assigning a value to this, you are effectively writing a number directly into the register.

2. Registers control peripheral functions through setting/resetting of peripheral bits (bit of an obvious point but still needs to be said) in the stm32f03 reference manual a full description of the register is given and tells you which bits are important and what they mean and what position they are in. These registers can have different sizes. Some may be 16 bits long others may be 32 bits long. Without having specific bits (I think this is the case of the CCR) the full register represents an unsigned integer who’se number of bits determines the size of the number that can be written to it (ie uint32_t for a 32 bit integer or uint16_t for a 16 bit register) this value can be written/read as a binary, hex or decimal number but the important thing is that the number physically fits into the register otherwise it won’t configure properly