If we are doing SEO then we should also understand algorithms of search engines, if we don't understand it then it may be very hard to earn from it, mainly we should understand algorithm of Google and Yahoo, they are really very popular search engines all over the world.

You should understand algorithm of Google mainly if you don't understand it then you may not earn much from Google. And it is fact that lots of people are making good money from Google only.

Both have their own algorithm so their algorithm may be different but you have to follow whit hat method for this first.

Yes, both have their own algorithm and you have to understand them if you don't understand then you would not be able to optimize your site in any search engines.