Just started with Linux and am eager to increase my knowledge in Linux. My question is, Are Linux command same in all distributions?

Welcome to the forums!

The basic terminal/command line commands (Bash shell) are the same in all Linux distributions. There are minor variations (for example in Debian you install packages with 'aptitude' and in Fedora you use 'yum') but for the most part skills you learn in one distro will transfer to other distros.

Some of the networking commands and hardware status commands are different in different distros, but mostly (80++%) they are the same. And sometimes different versions of the same command have different command options, with the more recent versions usually having more extensive lists of command line options. And for some of the more marginal commands, it depends on what you have installed, above and beyond the default set.

In any case, the man pages should describe exactly what you've got (although, some times the info pages are more up-to-date, or more comprehensive if you can live with those), and 'man -k' is always a useful start.