If four groups (2 cell lines +/- treatments) of single cell RNA seq available, do I have to analyze each of the four datasets seperately?

I have our groups (2 cell lines +/- treatments) of single-cell RNA seq data. I used cellranger count and cellranger aggr to generated the aggregated results.

How can I use these results for Seurat analysis?

Seurat has the following tutorial.
satijalab.org/seurat/articles/pbmc3k_tutorial.html

This tutorial seems to analyze each group of samples. And, it seems that it is not an analysis done after merging data matrices from all four conditions. Instead, it seems to analyze each data matrix separately. Am I right?

Do we do differential expression analysis like in regular RNA-seq?

Now, should I run each of the four groups of my dataset separately through this tutorial?