We use the past continuous to talk about events and habits that were happening at a certain time in the past. We also use it when two things are happening at the same time in the past. For example: We were watching TV when my friend came round.
We use the past simple to talk about events, states or habits at specific times in the past that happen after one another and are completed. For example: Yesterday I went to school.
How to form the past continuous: Use the simple past of "to be": "was" for I and he/she/it and "were" for you, we and they and then add "-ing" to the verb.
How to form the simple past: For regular verbs add "-ed" to the verb. Be careful with irregular verbs! Learn them by heart!