Official Missions

- The Twelve Portals -

The very first mission W.i.t.c.h. receives from Kandrakar is to find and close the 12 portals leading to the Metaworld. This seems to have been the purpose and constant mission for every guardian generation since their creation many thousands of years ago.
To help them with their mission, W.i.t.c.h. receives the map of twelve portals from Yan Lin but they complain about the questionable usefulness of the artefact.

It might be important to mention that W.i.t.c.h. was supposed to close the portals, NOT step through them (read more under "Broken Laws" below).

1. Portal - Sheffield Institute gym 

The first known portal is opened by Cedric and Vathek in the school gym shortly after the Halloween party. Only Will, Irma and Hay Lin see it and transform for the first time. The portal seems to open in order to lead the two Meridians back to their world but it closes fast and a fire has started in the gym. In the end, either the portal closed itself or it was destroyed by the fire.
The three W.i.t.c.h. girls end up detransforming automatically right after the fight and have to hurry out to not be caught in the blaze.

2. Portal - Elyon's house

The second portal appears in the catacombs under Elyon's house. She opened the portal and also closes it in order to escape from the battle with W.i.t.c.h. but apparently it is not destroyed completely.
Later Will can reopen it thanks to the Seal of Phobos locked inside the Heart of Kandrakar. Taranee extinguishes the blue white flames and they cross over to Meridian for the first time. The motive is mainly curiosity and also the attempt to find Elyon and sort things out.
But Elyon and Cedric are already waiting for them. In order to escape, Will creates the first version of astral drops to serve as decoy but Taranee is caught and imprisoned. The other four girls flee and create an actual more perfected astral drop to take Taranee's place in Heatherfield. Another act against the laws of Kandrakar and the girl's first failure.

After fleeing it is not shown how the portal is closed and for their next trip the W.i.t.c.h. girls use a different portal.

3. Portal - Ms Rudolph's House

The third portal is in Ms. Rudolph's house, a math teacher at Sheffield Institute who really is from Meridian and helped bring Elyon to Earth many years ago. After effortlessly trying to convince the girls of her good will, Ms. Rudolph flees through a portal in her attic. Irma wants to follow her but Will says they should focus on closing the portal.
This is interesting since shortly after, they go to Elyon's house and reopen the portal and use it to walk through. So while they do as they're told here, they go rogue right afterwards.
The portal closes after W.i.t.c.h. strikes it with united powers with a sort of implosion, sending the girls through the air and immediately detransforming them.

When W.i.t.c.h. sets out to rescue Taranee, they try to reopen the portal but for unknown reasons it doesn't work. Which is why they consult the map of twelve portals in order to find a new one.

4. Portal - Sea Shell Cave

The fourth portal looks and works very different to the others. It is located in the Sea Shell Cave of Heatherfield. It is marked by four blue flames on the cave walls and activates when the girls hold hands and focus, Will touching the scribbles. Instead of a firy ring however, this time the element is water which comes rushing through the cave. Irma creates a bubble to protect her friends and they are carried through the water into a sea shell in a fish bowl in Meridian. They break free and set out to help Taranee. Before leaving Heatherfield all four of them create real astral drops for the girls time. The oracle admires their new learned skill and precision but he's not happy with the results. It is possible he already forsees the dramatic turn of events connected to the astral drops.

The portal isn't closed officially.