To extract a tar ball, use tar utility in linux.

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$ tar -xzf ./go1.12.6.linux-amd64.tar.gz

This will unpack the go folder in the working directory.

To unpack it in a custom folder:

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$ tar -C /home/ashokma/go_1.12.6 -xzf ./go1.12.6.linux-amd64.tar.gz

Tip: Use -v option to see the list of files being extracted. It means be verbose about it!