Past Tense Vs Past Continuous

Past Tense: The event which is just happened and finished
Past Continuous Tense : The event still continuous, and didn't yet finished

The conjunction are:
While and When

When is usually followed by PAST TENSE
While is usually followed by PAST CONTINUOUS TENSE

Example:

• We had a flat tire while we were crossing the bridge
• He was having a good time when I saw him at the party
  
• Paul was writing a novel the last time When I saw him
• The idea came to me while I was driving
  

The pattern:

• _______ when Subject + V2 + C
• When Subject + V2 + C , ______
• _______ while Subject + was/were + V-ing + C
• While Subject + was/were + V -ing + C , S + V2 + C