While past participles can be used as verbs in their own right (e.g., "He had walked to the store"), they also play a crucial role in forming:
* Past tense verbs: "He walked to the store."
* Perfect tenses (present perfect, past perfect, future perfect):
* "I have walked to the store."
* "I had walked to the store."
* "I will have walked to the store."
* Passive voice: "The letter was mailed yesterday."
So, while adding "-ed" does create a past participle, it's important to understand its wider function in grammar.