A Bio Android's DNA is made up of the combination of many other race's DNA, so the resulting being has all the abilities of the said races. They can also take on characteristics and gain the knowledge and abilities of the individual "donors".
Bio Androids gain in power by absorbing what is referred to as "bio extract", meaning anything biological (eg. a Human or a Saiyan). To absorb the bio extract in this way, the Bio Android will stab it's tail into the victim's body, which it then sucks up through the tail, from the inside out. Only the clothes are left behind. After doing this, the Android's power level will be increased by approximately the same amount as the victim's power level. Only the Android's power level is affected using this technique.
They also have the ability to absorb, or "merge with" other Androids. They do this by sucking the Android up whole, through the tail, live and kicking. Once they have merged with an Android, their power will increase in the same manner as before, but their body and mind take on some of the characteristics of the Android. This technique is extremely effective, and the Bio Android is seen to evolve in the process.
Although they are Androids, they have no mechanical parts to speak of. They are entirely biological.