hi guys i need some help here, i dont know how to use transistors but i need to know how can i make a common emitter amp to energize a 6v relay via pic16f84a's voltage output

 

Do you have a 6V power supply? Maybe whatever is powering your IC?
And, how much current does your relay require?

 

5a and i tested that i can use 5v to energize the 6v relay

 

It's acceptable to run a relay at a voltage below it's nominal rating as long as it still meets the pick-up spec.

A 6V relay can use a significant amount of current (1/10 and amp) so a pin cannot drive it directly. Shown is a little transistor switch to drive the relay from a PIC pin (Px). Q1 isn't really critical so just about any NPN will do. R1 is a min value, 1K may be easier to find and will work well. D1 is a beefy rectifier type but a 1N4148 signal type may also work.

Don't leave D1 out as the circuit will seem to work... for a while until Q1 dies.

 

5a and i tested that i can use 5v to energize the 6v relay

5A !? That seems like a lot. It it's real (check again, I doubt it), be sure your power supply can handle that. Maybe the 5A is for the switching capability of the relay, not what it draws?

That transistor probably won't be big enough for 5A and you'll need a darlington since the transistor will need about 1/10th the relay current on its base, or 0.5A if the 5A rating is correct.