Do I need to collect sales tax on what I sell?

It depends on what you sell and where your customers are. Sales tax is a state and local matter, and rules vary widely. Generally, tangible goods are taxable and many professional services are not — but some states tax certain services and digital products, so don't assume. You collect tax in states where you have "nexus": a physical presence like an office or inventory, or "economic nexus" from exceeding a sales threshold in that state (commonly $100,000 in sales or 200 transactions, though the figures vary). If you have nexus, you must register with that state, collect the correct rate, and remit it on a schedule. Pure service businesses often owe none, while e-commerce sellers frequently owe in multiple states. Because penalties for not collecting fall on you, check your specific state's rules early and use sales-tax software if you sell across state lines.