In order to write an essay about adoption versus abortion, you first want to list the pros and cons of each choice. Presumably, the situation you are describing is one in which a woman has found out she is pregnant. She does not, for whatever reason, feel she can keep the baby. Therefore, she has to decide between carrying the pregnancy to term and giving up the child for adoption or terminating the pregnancy early on. I will list some of the pros and cons that come to mind. I am not passing moral judgment.
One pro of abortion is that the woman would not have to face the possible health risks of carrying the baby to term. You might want to look up the risk of injury or death from giving birth. This establishes that bearing a child is not risk free, especially in countries with limited access to healthcare. Another pro is that the woman might be able to move on with her life more quickly after an abortion.
The possible con of abortion is the "what if" question (what would the baby have been like, and will I regret the decision?) and the religious or ethical remorse that might arise.
A pro of adoption is the good feeling that might emerge from providing a childless couple with the chance to be parents, the chance to meet and pick the parents, and the possible opportunity to have some involvement in the child's life while not having to take primary responsibility. Cons might be the risk factors of carrying a baby to term or a deep anguish upon giving up the child.
Making a choice about whether or not to bear a child is a serious one. It might help to go online and see if you can find personal stories or narratives of women who have made these choices. This way, you can understand first hand why they made the decision they did, what factors were involved, and how they feel about it now. You will likely come up with a much longer set of pros and cons this way.