In written English and spoken English, a mix of past, present, and future tenses are used to describe past events. Ex: My uncle died last Monday and his funeral is tomorrow. He was a wonderful man who we will miss. (note - whom we will miss is archaic and rarely used now) For summarizing a book or a movie, or telling a joke, the simple present tense is normally used ("narrative present tense" or "historical present"). Ex: A man and a dog walk into a bar. The man orders a beer. Then, the dog orders a beer. Surprised, the bartender says to the man, "your dog talks!" The man says.... Here is more information: https://christinarebuffet.com/blog/past-tenses-in-english/ https://en.wikipedia.org/wiki/Historical_present

I was going to a shop and saw.... Seeing happened in the process of going ? - possible, but strange I was going to the shop and saw an accident on the street. I go to a shop and I see... Strange. Well, yesterday went like this: I go to the shop and I see an accident - As if a narrative - using present in the frame of reference of the narrative present? . As Sylvia says, past is more common. ... I went to the shop and there I saw this wonderful skirt/phone/car/dog.

I was going to a shop and saw..

I go to a shop. I see a book. I buy it. (three sequential actions - unusual wording) I went to a shop. I saw a book. I bought it. (three sequential actions - usual wording) While I was going to a shop, I saw a car accident. (two overlapping actions - usual wording).

What's the question?