As a 10th grader, you have some time before you need to start actively applying to colleges. However, the spring of your 10th grade year is a good time to start preparing for the college application process. Here are a few things you can do:

Start exploring your options: Use this time to start exploring different colleges and universities that interest you. Consider factors such as location, size, academic programs, and extracurricular opportunities. There is no need visit tons of campuses, but start to get well versed in the lingo of research university, liberal arts college, general education requirements, Greek life etc., will help ease the learning curve later.
Focus on your grades: Your grades are a crucial factor in the college admissions process, so it's important to focus on your studies and maintain good grades. It’s an important year to solidify study skills, you will likely have a very challenging year in 11th grade, so now is the time to sure up areas you find challenging, either in content or related to executive functioning (organization, time management, essay writing, etc.).
Take challenging courses: In addition to maintaining good grades, taking challenging courses can also demonstrate to colleges that you are capable of handling rigorous academic coursework. Think about your course planning for 11th grade and be proactive about meeting with an advisor or counselor in your school to discuss your options.
Plan your standardized testing: Consider taking a practice SAT or ACT exam to get an idea of your strengths and weaknesses and to start to consider if you will want to go forward and prepare to take an exam. You can also begin planning when to take the official exams in your junior year. Also beware that the digital SAT will roll out in 2023 internationally and in 2024 in the US!
Get (more) involved in extracurricular activities: Being involved in extracurricular activities can demonstrate your interests and passions to colleges. Consider joining or starting clubs, sports teams, or volunteering in your community. Hopefully you are starting to get more of a sense where your interests lie, now is a great time to deepen involvement, ask who needs help, so later on you may be primed to take on leadership roles. Summer is also a great time to build and deepen your interests!
Build relationships with your teachers and counselor: Your teachers and counselor can provide you with guidance and support throughout the college application process. Start building relationships with them now (if you haven’t yet!) so that they can get to know you and provide you with strong letters of recommendation in the future.
Research scholarships and financial aid: It's never too early to start researching scholarships and financial aid opportunities. By understanding the financial aid process and what scholarships are available, you can begin planning for how to pay for college.

Remember, the college application process can be overwhelming, but starting early and being proactive can help make it more manageable.