Medical Mondays: What are hormones and how do they work?

I’ve been considering starting bioidentical hormones. Ever since my mid 40’s, I’ve been experiencing difficulty sleeping and on night’s that I actually I do manage to fall asleep and stay asleep throughout the night, I wake up the next day feeling fatigued and lethargic. A girlfriend of mine told me that it could my hormones. I’ve been Googling a lot lately and a lot of the information on the internet doesn’t really address the basics. My question is what exactly are hormones and how do they work?