I am new to single cell RNA sequencing analysis and have been stuck on how to convert from .bam files to a gene-cell expression matrix. I am currently looking at data from the site: https://trace.ncbi.nlm.nih.gov/Traces/sra/?run=SRR10349606. I have downloaded the .bam file, and have been following the tutorial https://scrnaseq-course.cog.sanger.ac.uk/website/construction-of-expression-matrix.html. The tutorial talks about how to go from a fastq file to the gene-cell expression matrix, however it is my understanding that the .bam file I downloaded has already been aligned to a genome. I also looked into using featureCounts (bioconductor), but this required a cellbarcodeList, which I am unsure how to obtain.
Can someone point me in the right direction? I think I have a conceptual misunderstanding about this process.