Opera browser by default doesn’t have the search box enabled.
Here is how to enable it :
Access settings by typing in the address bar :
opera://settings
Next, choose Settings > Browser.
From the User interface section, select Enable search box in the address bar.
The search box will now be visible next to the address bar.
By the way, Opera has some cool  features too like free built-in VPN browsing and currency converter.
All done.
well can i change the search box well by default ‘google’ is set.
Yes you can.
Go to Menu(the Opera icon) >Settings > Browser and then from Search section : Choose the drop-down where it’s Google Search and choose any other as needed.