There are 2 methods to add your logo in a quote or invoice:


Method 1 - Quote Template: The easiest way is to add your logo directly on the quote template. 

Go to Biz Setup -> Quote Template.






Method 2 - Business Profile: You can also add your logo into your business profile section 


Biz Setup -> Biz Profile .  Here, just click in "+Add File" and select your logo.