It's an ancient ritual used mostly by alphas, since it's a skill that requires quite a bit of practice. One slip, and you could paralyze someone. Or kill them. - Peter Hale
Werewolves can meld their minds with those of others by inserting their claws into the recipients at the base of their skull.
Mind melding is used exclusively by the most experienced of shapeshifters, or alphas, as it is a dangerous act to perform. If not performed properly, the ritual could kill the recipient, paralyze them, or render them catatonic. If the process, the bond was broken by an outsider, it could kill both the user and recipient.
In 1x10 - Co-Captain, Peter Hale shared his memories of the Hale Fire and his coma with his werewolf progeny Scott McCall. Later in 3x02 - Chaos Rising he was able to partially uncover some of Isaac Lahey's memories that had been wiped by the Alpha Pack.
In 3x22 - De-Void, Scott McCall, with Peter's instruction, performed this ritual with his claws in both Stiles and Lydia, and so he and Lydia were able to both enter Stiles' subconscious, with the intention of splitting Stiles from the Nogitsune. In 5x08 - Ouroboros, Scott tapped into Corey's memories in an attempt to find the Dread Doctors' lair.