了 (liǎo / le): [makes an exclamation] — Stroke Order & Writing Guide

A sentence-final 了 often means the situation is now different: something started, stopped, became true, feels stronger, or is about to happen.

Some common words contain neutral-tone 了. In 为了 and 除了, learn the whole word instead of treating 了 as a sentence particle.

When 了 is pronounced liǎo, it often means understand, finish, settle, become clear, or be able to complete/endure something. This is different from the neutral-tone particle le.