Off topic:How to find differential gene expressions

Question

[Raz]

Hi, I am a mathematician and new to mRNA analysis. I am analyzing some mRNA seq data. My data set contains four-time points. in each time-point, I have 200 cells and 10000 genes. I need to find the differentially expressed genes between each time point. First of all, I would like to know, how and by which method I can find these genes? I mean statistically how it works? Second, I would like to convert this data set as annData in scanpy, but I do not know how should I do it? I would be thankful if you can give me a hand on it.