For guys, the only free health screening you can do yourself at home is to check yourself for testicular cancer. You should do this when your testicles are loose and descended, which means when you’re warm and relaxed, such as after a shower. Your nuts should feel like very smooth, firm, walnuts that slip around easily inside the scrotum. If you feel any kind of unusual lumps or hardness, get checked out by a doctor, since it could be cancer. Likewise, if you feel something like coiled string or worms in the scrotum near one or both testicles, you may have a condition called varicocele. This isn’t a medical emergency, but it can hurt your fertility. Again, seek a professional opinion.
If you want to spend some money, there are home health screening tests for a huge range of conditions, including high blood pressure, cholesterol levels, HIV status, thyroid function, PSA levels, and much more. All such testing kits must be approved by the FDA, but that does not mean they all produce equally meaningful or useful results. Unless privacy is absolutely necessary, I suggest you visit a doctor and talk about what tests you want. With issues as big as cancer, heart disease, or genetic problems you don’t want to fool around with tests that may, or may not, be accurate.