How Do you Find The Right Resister to use, for the transistor BASE, and to calculate the Base and collector current, is there a modified ohm's law formula?
If you want to use the transistor as a switch, then the 2 replies you have already received are correct. But if you want to use it as an analogue amplifier, then the answer is a bit more complicated. Too complex to explain here.
If this is the case, send me an email and I'll help.