What is difference between several mRNA RefSeq for one gene?
I'll walk you through the process of determining this:


Note that there are two gene names presented: HLA-F and HLA-F-AS1. The "AS" part means, "anti-sense", so it's on the opposite strand...so ignore all of the HLA-F-AS1s.
Note the associated chromosomes. chr6 is a normal chromosome, but things like chr6_cox_hap2 aren't. Instead, these are haplotype patches/chromosomes. The HLA regions are highly variable, so having only a single reference sequence ends up being problematic in many analyses, such as finding sequence variants. For your purposes you may or may not want to ignore these, it depends on what your goal is.
If you ignore the haplotype patches then you're left with 3 listings on chr6. These are the 3 isoforms of HLA-F. You end up needing to use the refseq IDs for each of these.


BTW, Gencode/Ensembl list 4 isoforms for HLA-F, rather than 3. Whenever UCSC disagrees with Gencode or Ensembl, go with Gencode or Ensembl.