How do I know what letter goes with what measure (music)

i would love to you but i cant see a picture. i see that you already told someone before that i wont let post pictures on well i can kinda of you. posting pictures on here with your question is so much easier if your posting them on the app on your phone. if your trying to post a picture on a computer what you have to do is find out the name of the painting or equation, and once you've got that go to google type in the name and ta-da! and then last but not least you have to copy it. at the bottom of where you typing out the question you sould have this thing that looks like a paper clip and hit that and it should let you add it on here.

i hope this

have a great day