extract what ? the first file is a bgzip file, the second file is its' index.

@OP: There is no point in extracting or viewing or doing any thing with .tbi. It is an index file of vcf.gz. For extracting .gz file, do gzip -d resources_broad_hg38_v0_1000G_phase1.snps.high_confidence.hg38.vcf.gz. This would extract vcf which would be larger. However, do not extract unless there is a valid reason to do so.

To extract the gz, see http://www.htslib.org/doc/bgzip.html

To retrieve data from the associated tbi, see http://www.htslib.org/doc/tabix.html