Your question isn’t entirely clear, but I believe you are asking about the verb forms. I’ll explain this sentence with that in mind:
“Two men were seen running after robbing the bank”
THE SHORT ANSWER
“Were seen” is the only verb phrase in this sentence. So conjugate this verb as you would conjugate a passive voice verb. “(Be) (past participle)” makes it “Were seen.”
THE LONG ANSWER
“Were seen” is the simple past tense passive voice form of “seen.” You seem to be familiar with passive voice, but for anyone who isn’t, I’ve linked an answer that explains it below. (1). This clause means “(Someone/something) saw the two men.”
“Running” is the present participle of “to run.” Present participles act as adjectives. The sentence now means “(Someone/something) saw that two men were running.” More present participle examples:
- “I see Jack eating” = “I see Jack; he is eating”
- “Panting, Usain sees the finish line approaching” = “Usain, who is panting, sees that the finish line is coming closer”
The entire sentence could work as “Two men were seen running.” But we don’t know when they were seen.
“After robbing the bank” tells us what time it is. This entire phrase is essentially an adverb telling us what time they were seen (it is technically a prepositional phrase). (2), (3).
“Robbing” in the above phrase is a gerund, which means it acts like a noun. It replaces the words “they rob/robbed/will rob” The sentence now means “(Someone/something) saw that two men were running, and this was after they robbed the bank.”
I hope this helped. Leave any questions in the comments
(1) Passive Voice Answer
(2) “Telling” in this sentence is a present participle meaning “that tells.” It’s the same for “meaning” in the previous sentence.
(3) Fun fact: “run after” can also be a phrasal verb that means “chase.” E.g., “I am running after my dreams!”