"Run" is the present tense of the verb. Use it for:
* Present actions: "I *run* every morning."
* Future actions: "I will *run* a marathon next year."
* General truths: "Dogs *run* on four legs."
"Ran" is the past tense of the verb. Use it for actions that happened in the past:
* Simple past: "I *ran* a mile yesterday."
* Past continuous: "I was *running* when I saw the dog."
Examples:
* Present: "I *run* to the store for milk every day."
* Past: "I *ran* a marathon last weekend."
* Future: "I will *run* in the park tomorrow."
Important Note: "Ran" is also the past participle of "run" (used with "have," "has," "had"). For example:
* "I have *run* a marathon before."
* "She had *run* five miles by the time I caught up with her."