Past tense, for regular verbs, uses "-ed" at the end of the verb. An example of the verb "walk" in past tense is "walked." Past participle requires something called an "auxiliary verb."
What's an auxiliary verb? In this case, it's usually "have" or "had."
Here are examples for the verb "walk":
Past tense: "I walked to the park with my friends."
Past participle: "I had walked to the park with my friends."
Past participle is usually used when events happened recently, whereas past tense can be used for any event that already happened in the past no matter how long ago.