Yes. You have to file if you had over $400 of income from working that you did not get a W2 for. An employee getting a W2 has taxes (SS & Medicare) taken out for them. If you are self employed meaning you are working for yourself you have to pay in both the employer share and your share of the FICA (SS & Medicare). That is the SE tax.
If you are not paid as a W2 employee with taxes taken out then you probably file as self employed. You might get a 1099Misc for the income. You need to keep good records and report all your income, even if you don't get a 1099Misc. You fill out a Schedule C in your personal 1040 tax return and pay Self Employment Tax in addition to regular income tax on it.
When you are self employed you are in business for yourself and the person or company that pays you is your customer or client.
To report your self employment income you will fill out schedule C in your personal 1040 tax return and pay SE self employment Tax. You will need to use the Online Self Employed version or any Desktop program but the Desktop Home & Business version will have the most help.
Being Freelance or independent contractor, outside consultant, sub-contractor, sole proprietor, self employed, etc. are all the same thing. You need to fill out schedule C for self employment business income. You are considered to have your own business for it. YOU are the business.
See Are you an Employee or an Independent Contractor?
https://ttlc.intuit.com/community/self-employed/help/am-i-an-employee-or-an-independent-contractor/0...
