If my brother transfers money to my account. How does the tax work ? Do I have to declare that amount as income from other sources to CRA ? or report as just gift ?

If your brother is just transferring money to you for personal reasons, it is not considered as income and you do not need to report it all.

@TurboTaxMary-Ann1 @Thanks for the response

If it's by any other friends within canada or us. How we have to look those transactions ?

If you have friends sending you money from Canada and the US - Depending on the reason why they are sending you money,  you may need to claim it on your income tax return. 

Click here for more information from CRA on what you must report.