A lot of questions here! Firstly, your question rewritten: "I have seen Youtube videos using this tense, and I think there are clues that would help me understand more easily." 1/ In this sentence "i was studying a fun English lesson when you came up to my lovely house last night." You are using the past continuous to describe something that was happening, then this action was interrupted by some event, using the simple past, "you came to my house". This is simple past tense, not the past participle. You can use the past continuous in other ways, for example, "I was working from morning till night". No nterrupted action here. 2/ "While i was doing my math homework, my brother was playing with his new expensive toy car." this is using the past continuous for both actions, 2 events happening over a period of time simultaneously. "my mom went to the fruit market while my little sister was sleeping" this is past continuous and past simple, thesame as the interrupted action with "when". 3/ Both tenses sound right, it depends on what you want to say. if you use "was falling"you are narrating events over time in the past, telling a story. If you say "it was Sunday morning, the rain fell" it means the same thing, but using the past simple "fell" , you could think of this as though suddenly the rain fell, an event, or use fell instead of was falling for literary effect. Phew!