Poppers are frequently used by fisters to relax and open up. It comes in small bottles. You open the cap and inhale the vapour. You feel the effect immediately.
Like all drugs, you need to read about the risks. It certainly is not harmless!
You can’t use poppers together with other products that lower your blood pressure, like viagra / kamagra. This combination can kill you!
Just do a google search about poppers to inform yourself.
Poppers explained in English on Wikipedia
Poppers uitgelegd in het Nederlands op Wikipedia