Unable to select one object without selecting the whole art piece

Hello,

I'm very new to illustrator and I don't know the program very well. I have been plugging along and editing one element at a time, but now the selection of one object continues to select every object in the whole art piece. This makes it unable for me to keep editing one piece at a time. Not sure how to get it to go back and allow me to edit one element at a time. No matter what I click on it continues to select everything. Any thoughts? Thank you