Hello I'm new to survival analysis and I have a question about right censored data processing.
For patient B, he survived through the entire study time. Therefore, we need to use the study end date to subtract the study start date to extract the survival days for patient B?
You don't have the survival time; your information is that you started monitoring the patient at time $t_0$ and at $t_{end}$ was still "alive." Thus, if $T$ is their survival time, your information is $$ P(T > t_{end}). $$ where $$ P(T > t_{end}) = 1 - P(T \le t_{end}) = 1 - F(t_{end}) = S(t_{end}). $$ Namely, you know that their survival time is at least $t_{end}$ time points, but you cannot know its exact value (hence, the term censoring").