My knowledge of statistics is limited and I am looking for resources to read on the matter if possible.

Anyways, I am currently trying to estimate a confidence interval for a proportion over time. The specific example pertains to a trader's Win % as he make more trades. My current idea is to take the first $n$ sample data to calculate a proportion, then see how that changes over the amount of trades. I want to ultimately calculate the variability of the win %. My confidence interval would be calculated as such:

$$p \pm \sqrt[2]{\frac{1}{n} * p(1-p)}$$

I know this is clearly the wrong approach to look into but I would appreciate it if I am pointed to in the right direction.