The "open()" function in Python is used to open a file and returns a file object. It takes two arguments: the filename (or path to the file) and the mode in which the file should be opened.

Here's an example of using the "open()" function to open a file in read mode:

file = open("example.txt", "r")  
# Perform operations on the file  
content = file.read()  
print(content)  
# Close the file  
file.close()  

In this example, we open a file named "example.txt" in read mode ("r"). We read the entire content of the file using the "read()" method on the file object and store it in the "content" variable. Finally, we print the content and close the file using the "close()" method.