How do I use slicing to select a portion of a DataFrame?

Slicing allows you to select a subset of rows and columns. The syntax is `df[start:end, start:end]`, where `start` and `end` define the starting and ending indices (or labels). For example, `df[0:3, 'col1':'col3']` will select rows 0 to 2 (inclusive) and columns 'col1' to 'col3' (inclusive).