@hrsagar first, I assumed you’re asking as a user. So:
In order to get “rewards” / earn BAT, you need to opt-in to Brave Ads (available for desktop and Android in supported regions). Brave will show you an ads as system notification.
You can have Brave Ads enabled with Auto-contribute disabled.
They are two different feature with each own setting. Brave Ads is a feature to earn BAT while Auto-contributr is a feature that allow Brave user to support online creators. But it’s better if you also support online creators.
Auto-contribute and tipping will use funds that you have on your brave://rewards wallet. Either it’s BAT from grants, from ads or your own funds.