Hi, I am new to bioinformatics. I am trying to understand the meaning of chromosome column. Except for the common 22 pairs of chromosome and X, Y, some other chromosome names are strange to me like CHR_HSCHR17_2_CTG5, MT, CHR_HSCHR8_3_CTG1, CHR_HSCHR7_3_CTG4_4... Could you please advise some introductory materials? Thanks!

Your question is way off topic for this site. You would probably do better to search biostars.org. Or simply look at the GRC site, which is where those data originate, particularly the link for alternate loci. There is a slideshow that may be helpful as well.