I guess you are in your free starter sidewinder. You were docked somewhere else, and used outfitting to remove your docking computer module (and maybe some other stuff) and then flew to & docked at another station. You used outfitting in the starport services menu to remove the module & store it, you used it again to pay to have the module transferred to your location at the time.
Have you flown to another location since transferring the module? If so, go back there, open Starport Services and click on Outfitting (in ship services, lower right of the starport Services screen).
In Outfitting you will see some choices on the right (first one is Hardpoints), click on 'Optional Internal' and look at the bottom of the list of slots.
The lowest one will be 'Planetary Approach Suite' (unless you removed it), the next one up is where your docking computer was.
Assuming that slot is currently empty, click on it, then choose 'Transfer Options', 'Transfer' and you should see a list of locally stored modules (in your case I'm guessing you will only see one, the docking computer you paid to have transferred to that station).
Equip the module (click on it & choose 'Transfer to Ship') & voila you should have autodock again
When you have just started a new Cmdr, that's the ideal time to try stuff & make mistakes, because even if you screw everything up you can reset your save, losing all your progress so far & just start again & with your newfound knowledge hopefully not make those mistakes again. Make different ones

.
The longer you keep playing one Cmdr the more you will lose if you reset so now is the ideal time to really, really make a mess of things.
You will get better, it is a complex game to start but the initially steep learning curve levels off pretty quickly.
Good Luck!