How do I pull singe cell RNA sequencing data from GEO database?
The simplest would be using a count matrix (at the end of the link you have shared, section "Supplementary file"). For example GSE138651_Vagal_WholeNodoseSeq_raw.mtx.gz corresponds to "raw" count matrices obtained after mapping and counting the reads. This file, along with the GSE138651_barcodes.tsv.gz and GSE138651_genes.tsv.gz can be used to "read" the data into R; to that end there are many options in the form of packages, Seurat is one of the best documented and hence is beginner-friendly.