The Common Application is a generic online college application accepted by over 800 U.S. colleges & universities. It allows students to apply to multiple colleges (up to 20!) through just one application, and includes sections for: Family, Education, Testing, Activities, Courses & Grades, Essay (choose from 7 possible prompts) and a section where you list a counselor* and teachers to write you recommendations. The counselor also uploads your official transcript here.
You can create a Common App account as a junior, if you like, and start reviewing what it contains. Don't fill it out until after Aug. 1 of your senior year fall, though, because Common App resets applications when it reboots on Aug. 1 of every year.
Contact your counselor or Ms. Velhagen -- whoever knows you better -- to discuss your Common App Counselor Recommendation and School Report (including official transcript upload). Please give teachers and counselors a minimum of three weeks' notice when asking for Common App (or any) recommendation letters, and check in with them re: what they require from you (often a resume, personal statement, questionnaires) and how you can help them write you a detailed and supportive letter.
YOU MUST order your own ACT and/or SAT scores directly from the testing companies and have them sent to your Common App colleges.