If you are not an employee, your employer should issue you a 1099 Form to report $ paid to you.
Very important: SAVE a portion of every $$ you get paid in a savings account, and do not spend it for anything except your tax obligation, classes, memberships, etc. I put 25% in mine, last year was 30% but I determined it was higher than necessary. If you don't SAVE now, you will have to SPEND later, and may even have to take out a loan to pay your tax obligation. That's not smart! Learn to live and play on the net $, and you won't stress about taxes!
As Terrel says, keep track of all business expenses and mileage. I use a monthly sheet for mileage to show the date, mileage in/out, file # and location of each assignment...and travel to classes, etc. IRS requires a written document for verification.
Keep a file folder just for your business. All receipts go in it as acquired. At tax time, sort it all out...mileage in this pile, tallied; cell phone bill in this pile, supply receipts in that pile, tallied; etc., etc. That's what your CPA or accountant will appreciate, and will probably save you money on their fee.