Simple:
* I'm bored and don't know what to do.
* The lecture was so boring I almost fell asleep.
With more detail:
* After a week of rainy weather, I'm bored out of my mind.
* The movie was so boring I started doodling on my notepad.
* My friends are going out, but I'm too bored to go.
In different contexts:
* Bored with the same routine, she decided to take a trip.
* The children became bored with their toys and started fighting.
* The speaker's monotone voice made the audience feel bored.
Figurative Language:
* My brain was bored with the repetitive tasks.
* The room felt boring and lifeless without any decorations.
You can use "bored" to express a feeling of lack of interest, stimulation, or excitement.