Question

I need help to understand the following command.

tar -cvf /dev/nst0 /home/user1 >> file1.log 

Answer 1

Read the man page :

-c stands for create -v is for verbose -f specify the archive name 

And tar -cvf is equivalent to tar -c -v -f, so what this is doing is creating an archive of /home/user1 into /dev/nst0. The >> file1.log is redirecting and appending the standard output to file1.log. tar -cvf archive_name [files] > file.log would erase any existing content in file1.log

Have a look here for an explanation on I/O redirection