I am new to use unix operating system, and I was wondering where can start learning the main commands in the unix, as I am working on server that is unix,
tutorials or links that can help, when I need some functionality or a specific command I search the google , but this approach is time consuming, a reference would be helpful
You're probably already doing this, but I'll mention it to make sure.
Once you have a general idea of what command you might use, "man <command>" brings up a manual-page on that command. "man grep", for example, brings up a succinct briefing on the options and syntax of the grep command.
I don't know about the UNIX system you're using, but, on my Linux systems, "apropos" is a good search tool when you've got an idea of what you want to do but aren't sure what command to use to do it.
apropos filter | less
...will bring up one-line mentions of every tool whose man-page mentions the word 'filter' in the summary or title. If the system you're on doesn't have 'less', try 'more' instead. Either way, piping it into a pager like that means you can scroll around while making up your mind what to use out of what's available. As with Google searches, your first search term might not get you what you need, but it might suggest better search terms for you to use.