I am very new to unix and Linux, So I have a question about LINUX and AIX.
What LINUX and AIX commands can be used to get the following output:

071912 GB blocks Free %Iused Mounted on
071912 5.00 4.64 8% /
071912 15.00 9.44 38% /usr
071912 6.00 2.56 58% /var
071912 15.00 12.88 15% /tmp
071912 3.00 1.97 35% /home
071912 0.50 0.50 1% /admin

Another question is how to write a script which will give u a warning about the large files getting filled upto a certain level and send out emails to warn the user. I will appreciate the help thank you.

It is more likely a df command output. exact output and formatting slightly varies with the operating systems. Please try on your system and check the man pages for more details.

About the second requirement, You could use find command to find the files which are having huge (said) size.

Search for similar threads in this forum. you might get lots of stuffs there.

man df , man find and check for -size inside it and man mailx