Let's start with explaining what they are.
Affirmations are positive statements that describe a desired situation or goal, and are often repeated, in order to get them impressed on the subconscious mind. Repeating them motivates, inspires, and programs the mind to act according to the repeated words.
This process triggers the subconscious mind to strive and to work on the person's behalf, to make the positive statements come true.
When you know how to use affirmations, you posssess a useful tool for achieving success and for improving your life.
Most people repeat in their minds negative words and statements concerning the situations and events in their lives, and consequently, create undesirable situations. Words work at both ways, to build or destroy. It is the way we use them that determines whether they are going to bring good or harmful results.
Your subconscious mind accepts as true what you keep saying. It attracts corresponding events and situations into your life. So why not choose only positive statements, in order to get positive results?