How many injective maps are there from 1 2 to 1 2 3?

Could you please clarify for me how we can determine the number of injective maps that exist from the set {1, 2} to the set {1, 2, 3}? I'm having some difficulty grasping the concept of injective maps and how they can be counted in this particular case. Would you mind explaining the steps involved in calculating this? It would be greatly appreciated if you could provide a detailed and structured approach to tackle this question. Thank you for your assistance!