It protects your ownership right to your home both from fraudulent claims against your ownership and from mistakes made in earlier sales, such as mistake in the spelling of a persons name or an inaccurate description of the property.
Its a one-time cost usually based on the price of the property.
Its usually paid for by the sellers.
There are both lender title policies, which protect the lender, and owner title policies, which protect you. The lender will probably require a lender policy.
Discounts on premiums are sometimes available if the home has been bought within only a few years since not as much work is required to check the title. Ask the title company if this discount is available.