Affirmations are affirming something that is true. Something that is true yet unseen. When you affirm something you agree with the word of God. Affirmations should always be positive. And should always be spoken in present tense (example: by the stripes of Jesus I am healed-1Peter 2:24). Because the word of God is truth. And should be spoken as such.
Affirming in line with the word causes faith to come. And faith is the substance of things hoped for and the evidence of things not seen. In other words faith gives substance to the spiritual in the physical. But your faith has to be released by your words. And your words are creative. God created the world with his faith and words and you were made like him.
There is a system in the Bible that God uses and encourages us to use called- calling things that be not as though they were. Calling things that be not what? Calling things that be not in the physical realm. God's word is true now even though it may be unseen. Understand that God's word is a spiritual reality and the spiritual produces the physical. Everything originated from God who is a spirit. So when you affirm (call things) you are calling things from the spiritual into the physical. When you choose to affirm with faith you are choosing to believe God over what you see. And affirming with faith in line with the word of God causes the spiritual reality to be created in the physical world. The purpose of calling something is for it to come into your presence. So the thing has to be somewhere. And if you affirm (call) something long enough it will come. It will come from the spiritual into the physical. Just have patients and stay with it.