hello! i bought a laptop and i need to get a mic working.my problem is that the laptop has only on jack and if

Do you want to use the audio from your headphones and the laptop mic, or
do you want to use the audio and mic on the headphones.

Also, most new-ish laptops have the ability to use both a mic and headphones from the same port. If your port has a small headphones icon next to it, this should work.

I have Realtek HD Audio Manager on my laptop (as you likely do)
When you plug a new audio device (like a combined 3.5mm jack for your headphones) it will (most of the time) prompt you if the new device is:

-Speaker
or
-Headphones

If you pick speaker it will default to the mic on the laptop and the audio on the headphones.
If you pick Headphones it will use the mic and audio on the headphones

I dont know if you have this same sound manager, but if you do, you can force to prompt box to pup up
by following:

⊞>"Realtek HD Audio Manager"
Look for the panel on the right labled "Analog"
There should be a small folder in the top right corner of that panel.
Click it and enable "Enable auto popup dialogue, when device has been plugged in."

Hope this helps