Firstly download Alexa app in your device and Alexa app setup by doing Alexa login. Connect Echo to wifi and Add your details in the Alexa app. Select your Amazon echo dot or other echo devices from the list. You can get the Alexa app for echo, Alexa.amazon.com and Alexa app for pc.
Alexa setup is done by asking any questions to Alexa. By visiting the bellow website, you can know the steps for echo setup, echo dot setup, and many more. Also, Know the tips & tricks to use Amazon Alexa and Amazon echo.