Imagine you're at a party. Think about what you can see. In your mind you probably can see people dancing. There's some music playing. One of your friends is laughing. There are lots of people having a good time.
You were just imagining "having a party" from the inside of the experience. You didn't think about the beginning or the end of the party, or the effect the party had afterwards. In your mind, you were thinking about it in the middle of the experience.
Now imagine that you are a party organiser. Every week you have to organise a new party at your venue. Think about what you have to do. You need to buy the food and drinks. You have to send out invitations. You need to decorate the building. People will come to your party, have a good time, hopefully, and then go home. When it all happens well, you make lots of money.
You were just thinking about parties from the "outside". You thought about the beginning and end and the effect of the completed parties. You thought about whole parties. You didn't imagine just the middle. It wasn't like watching a little video of a few seconds during a party.
In English, we represent thinking about actions and events from the inside by using the "continuous" aspect. This usually involves the auxiliary BE and a verb in the ING form. We could represent the first idea we thought about like this:
We were having a party.
We could represent the second idea like this:
Every week we have a party.
When people study other languages, they often use different names for the "continuous" aspect. This can be confusing because these other words are used for completely different ideas in English grammar.