Most good quality movies are at least 1 GB of data in size.
So with 1 GB of data you'd only be able to watch only 1 movie before you use the whole 1 GB of your data.
Some lower quality movies may use a bit less than 1 GB of data but still you wouldn't have enough data leftover to watch another movie unless you have more than 1 GB of data left.
If you want to watch movies it's best to use unlimited WiFi instead of mobile data unless your mobile data is unlimited.