It isn't all that complicated for a sole proprietor, self-employed person starting out.
Building good habits is just as important as learning all the ins and outs. When you have kept good records all year, your quarterly and year end filings are much simpler than when you open up a shopping bag of disorganized slips, notes, and receipts on April 13.
Don't make yourself crazy trying to justify expenditures as deductions to make a few cents when you know there is no basis to that claim.
Keep records of all expenditures for your business pursuits. Start a file immediately, and notate on all receipts why the expenditure was a business expense.
I suggest a separate checking account and separate credit card just for business. You can make a mistake with a credit card, check, or paying cash for something. Just record it and move on.
Keep excellent mileage records. I use a GPS system that lets me record mileage very accurately, classified either as business or personal at the press of a button.
GPS Mileage Log Tracking - Car distance logbook - IRS Report
When you hang your license, all the brokerage costs you pay directly are business expenses. Keep a good file.
There is a trove of information on the IRS site regarding business expenses and filing:
Income & Expenses