The vapors from the product enter the lungs where the chemicals pass directly into the bloodstream and are quickly circulated through the body. Most inhalants are 'depressants'. This does not necessarily mean that they you feel depressed. They work by slowing down the activity of the brain and central nervous system. They slow down the messages going to and from the brain to the body.
Inhalants have similar effects to other depressant drugs such as alcohol and cannabis.
Any given amount may have a slight effect on one person, but a much greater effect on another person. Small amounts of inhalants can effect you quite quickly. It depends on how much is taken, how it is taken, whether the person is used to taking this, and the mood of the person and other factors. Like alcohol, inhalants can make the user less inhibited. They may laugh, become excited and generally feel intoxicated.