How to download Microsoft office 2016 or some equivalent? I am rookie with mac. 
I need to open Excel, Word and maybe I forgot about something else, but this two I really need.

After I look throw internet as far as I understood the most useable for this case it is Microsoft office. I found some video tutorials how to download it for free, but links that were provided by that tutorials now are disabled.

Could you please give me advice should I buy Microsoft office or maybe there are some other app?

Thanks in advance!
Try the free office clone LibreOffice

http://www.libreoffice.org