That's a big question! What do you like to do? Is there anything you have a passion for? Are you good in science or math? Do you like writing?
My oldest daughter knew she wanted to be a nurse. However, my youngest daughter wasn't sure what she wanted to be... Fortunately there are tests one can take that help show your strengths and suggest a career path. In my daughter's case, the college actually had them take these tests. As it turns out both of my daughters are nurses! I am so blessed!! Just say'n!!
You can start by identifying your interests, abilities, passions, etc. From there you want to thing about the future. Some people pick a school based on their major, some just pick a school. My daughters both picked a school/college and the oldest knew what she wanted to be a nurse. However, my youngest made that decision afterwards. It's good that you're thinking about it now!!
Sometimes students pick a major and then find they don't possess the skill set. If you know you're good a math for example and enjoy it, there's Physics, math and statistics, computer science, electrical engineering, economics, just to name a few. Some people like helping others. There's education, social work, humanities... The list goes on! So you'll want to consider this when choosing a major. And don't be afraid to ask for help! If you get into a major and find it's not for you. It's not the end of the world. You can change. During the first couple of years of college, you're mostly working on the essential classes that are required for just about every major.
Hope this helps!!