WElcome to the forum IM1,
Have you ever had your test levels checked? Are you interested in doing steroids, or TRT, or something non steroidal.
If finances allow, a TRT clinic may be the way to go for you. It's legal and if you shop around you can find one that costs about $150 a month.
As far as natural stuff, creatine will help you build some muscle, and Vitamin D is known to boost testosterone levels.
A good workout program and diet is the key for everything muscle related.
What are your current stats and more importantly your goals? Do you lift, crossfit, run, play sports? Just trying to put on some muscle or lose some body fat? There are many ways to go but a lot of it is about knowing where you wanna head and letting others help you get there.
+1. Definitely some pertinent questions to be asking.