You watch a lot of adverts on TV and on the internet. Are you sure you mean "watch"? That means that you actually concentrate on them and take notice of them. I would use "see" to indicate that they're on but we don't necessarily take any notice of them. I would say "There are a lot of adverts on TV and the internet".
When [STRIKE]we[/STRIKE] you watch a movie or series, adverts are broadcast in the middle. [STRIKE]of the movie or series.[/STRIKE
You started with "You" in the previous sentence so it doesn't make sense to switch to "we" here. There's no need to repeat "the movie or series". Saying "in the middle" means that the adverts appear exactly halfway through. Your next sentence contradicts that.
Every few minutes they broadcast adverts, which is annoying. See my comment above about how this is contradictory. They either broadcast adverts in the middle or every few minutes. It can't be both.
In Indian movies, after [STRIKE]a[/STRIKE] every few scenes you can see a song. Generally, we hear a song.
They put in a song after every few scenes.
Please correct my sentences.