Gmail is safest email provider and provide various useful functions but we still get thousands of spam daily. It is really hard to filter those junks and consume too much time.
But below are some tricks which can delete all those in minutes.
You need to Login in your account and open setting.
Now you need to click on Filters and Blocked Addresses option, create filters and popup window will open where you can filter emails.
If you want to only filter email of single email id which sends you bulk mails then you need to put its email id in FROM field and click on Search icon.
New window will appear with filtered email id, now click on SELECT ALL option and delete, it will save your time and effort.
You can filter by SUBJECTS and even you can filter by containing words in email.
Just test all fields one by one.