In Naruto, I have seen that to create summoning contract and to use summoning jutsu, the user uses their own blood.
Why is this required? What is the significance of using blood here?
You can read in the Wikia that
The Summoning Technique is a space–time ninjutsu that allows the summoner to transport animals or people across long distances instantly and uses blood as a sacrifice.
In more detail:
The contract comes in the form of a scroll, on which the contractor uses their own blood to sign their name and place their fingerprints and once signed it is valid even after the contractors death as long as the contract itself remains intact. After this, they need only offer an additional donation of blood on the hand they signed the contract with, mould their chakra with hand seals and then plant the hand they signed the contract with at the location they wish to summon the creature.
It should be noted that anyone can summon a contracted animal as long as they have the blood of someone who has made a contract, the seal of the summoned creature and a source of sufficient chakra that the summon will accept.
So basically, the blood serves as a means of identifying the summoner for the summoned and also acts as a price (sacrifice) for calling them.