You might want to untrack certain files and folders when pushing code from the local system to the scratch Org. To do this, you have to create a file named forceignore. The sample format for forceignore is as follows:

# Specify a relative path to a directory from the project root
helloWorld/main/default/classes

# Specify a wildcard directory - any directory named “classes” is excluded
**classes

# Specify file extensions
**.cls
**.pdf

# Specify a specific file
helloWorld/main/default/HelloWorld.cls