You will need a CSV file containing all of the searches you want to run in the bulk search. Use the guide for creating a Bulk Search template to make this.
Select Account from the top navigation.
Select My Searches from the account menu.
Select Saved Searches then Bulk Searches.
If you can not see bulk searches it may be that your administrator has not enabled this feature.
Select New Bulk Search
This will take you to a new Bulk Search, Search Details page.
Before processing bulk searched the job gets all the CSVs it needs to process. If you edit your settings or CSV while the job is running these changes will not be applied until the next time the search is performed.