You fill out Schedule C at tax time and attach it to or file it electronically with Form 1040. Schedule C is typically for people who operate sole proprietorships or single-member LLCs.

You can think of the 1040 like a math worksheet: You plug in various numbers from a schedule (Form 1040 will tell you which one to use) and add the schedules' totals to your Form 1040. Form 1040 ...