med1428 did a good job of describing typical symptoms. It can be tested with a simple blood test. If you're an adult the result should be over 200.
Hi, im a 30 yr old male and ive been diagnosed with low testosterone, i can tell u what my symptoms were and hopefully this will help u, i was tired and fatigued all the time i had no sex drive or no man type thinking, i developed flutters in my chest, and i always felt like i was out of it sorta, not to mention i was having emotional sensitivety problems almost like a woman's emotions and last but not least a weak ejaculation,but ive been on androgel for three months and i am feeling better, im having more of a sex drive, and really strong ejaculations my doctor upped my dose because im not at 100 percent yet but im definately doing better, hope this helps u.