Split Testing is basically duplicating a campaign or an ad group or an ad and changing one thing. It could be changing locations, keyword lists, headlines, etc.
The important aspect of split testing is to see which feature is the best. This test is a fantastic way to gather data and understand how to further optimize your campaigns.
In order to do split testing, you can copy the campaign, ad group, or ad that you want another version of and paste it. You just need to make the changes to the copy of your campaign and run them at the same time.