First of all we need to find out, what is a Link monster? What shape do they have? What's the difference? Why were they created?
Link Monsters are a type of card monster with a dark blue card frame color, similar to that of Ritual Monsters, but with a hexagonal pattern similar to a honeycomb structure. They first appeared in Yu-Gi-Oh! VRAINS anime, and was first introduced to the OCG and TCG in Structure Deck: Cyberse Link.
These cards are placed in the Extra Deck (different from the Ritual used in the Main Deck). Like other Extra Deck monsters, Link monsters cannot be returned to the hand or Main Deck (even with card effects). If a Link monster is returned to the hand or Main Deck, it is returned to the Extra Deck.
If a Link monster is not Link Summoned first, it cannot be Special Summoned from the Graveyard or while banished (unless it has another way to properly Special Summon in that card's text). .
One point that differentiates Link monsters from other monsters is that they have no Level or Rank (ie, no black or yellow stars). Furthermore, Link monsters do not have a DEF stat, meaning they cannot enter a defensive position. In the future, you can take advantage of these things for your plays.
Link monsters were created with the purpose of speeding up the game by continuously summoning monsters with the purpose of bringing up your main monsters. Furthermore, to support this, Konami has created many monsters with special effects that support their special summons. And since then, Konami has released a new type of card - Cyberse.