The Adrenergic Receptors Explained:

Many compounds, such as Epherdrine, Caffine (indirectly), Clenbuterol, Albuterol, Yohimbine, etc, work by interacting with the adrenergic receptors.

I found this video very helpful in understand these receptors and how various compound exert their effects:
https://www.youtube.com/watch?v=lV280wQYcU0

Further reading for each specific receptor (wikipedia)
Alpha-1: https://en.wikipedia.org/wiki/Alpha-1_adrenergic_receptor
Alpha-2: https://en.wikipedia.org/wiki/Alpha-2_adrenergic_receptor
Beta-1: https://en.wikipedia.org/wiki/Beta-1_adrenergic_receptor
Beta-2: https://en.wikipedia.org/wiki/Beta-2_adrenergic_receptor
Beta-3: https://en.wikipedia.org/wiki/Beta-3_adrenergic_receptor