Imagine that you're cleaning up data. You want to delete everything after the comma in every line of data.
Use the replace feature (control+h) in Notepad++.
Choose "Regular Expression" mode.
In "Find What" enter ",.*".
Leave "Replace with" blank.
Click "Replace All." Ever line will be trimmed to delete the end of each line.
The regular expression basically says: "Match a comma and any character that comes after it."
Note that the action replaces all lines and that includes the lines in these instructions. You could have selected the lines below and checked the box "In selection" to avoid messing up these instructions.

Name	Date of Birth	City	Longitude, Something I don't want
Alex Johnson	1995-07-15	Seattle	122.3321, Foo
Maya Singh	1988-02-28	Mumbai	72.8777, Bar
Ben Carter	2001-11-03	London	0.1278, FooBar
Sofia Rossi	1976-05-10	Rome	12.4964, Fizz
Kenji Tanaka	1999-09-21	Tokyo	139.6917, Buzz
Chloe Davis	1990-04-19	Sydney	151.2093, FizzBuzz
Omar Hassan	1982-12-05	Cairo	31.2357, Why is this data so messy?