When i type either a text message or email, every word begins with a capital letter. Why is this happening and how can i change it back to the original way when the first letter of the sentence is only capitalized. Can someone help me? Thanks

When i type either a text message or email, every word begins with a capital letter. Why is this happening and how can i change it back to the original way when the first letter of the sentence is only capitalized. Can someone help me? Thanks