Regex is a language that is useful to extract specific data from text into a list of things that are accessible from your Bubble app.
You can use a regex expression in Bubble to extract specific data directly from a text string using the :extract with regex operator and is likely the way you will use it most often. However, it can also be quite handy to use within the :find and replace functionality to identify the text you want to replace rather than typing in a static value.
The expressions below should work in both environment.

Convert comma separated values into a list of texts

Expression: [^\,]+
You may have a text string such at "Juan, Lola, Henry, Felipe, Tonya". Using this regex on this text will convert it into a list of texts which you can then sort, filter, etc in your Bubble app.
Replace the comma above with another character such as a semicolon or space for a list with a different separator.

Working with URLs

Sample URL:

Extracting a parameter value from a url

Expression: (?<={placeholder}=)[^\&]+
Replace the placeholder text in the expression with the name of the parameter containing the value you need to retrieve. For example this expression (?<=param1=)[^\&]+ will return 'value1' from the sample URL.

Extract file name extension

Demo String: myAwesomeImage.jpeg, favoriteVideo.mp4
Expression: (?<=.)\w{0,4}
Use this expression to extract the extension type from one file or a list of files. Running this expression on the above list of filenames would result in the following list of texts "jpeg, mp4"