* I'm writing in English so that you find easier to understand. If you prefer me to write in Spanish, please let me know.
Hello, MariDieMissy, nice to meet you!
The difference is easy to understand.
When you use "I was walking" you're telling an action that happened in the past but at that time was not yet finished. That was happening.
But when you use "I was walking", you are telling something that happened in the past and already concluded. That already happened.
In English is used the same tense for these two Spanish verb tenses, but in Spanish there is that subtle difference.
I sincerely hope this helps.
Best wishes.