A sole proprietorship is a business with only one owner. A [general] partnership has two or more owners. (There are other kinds of partnerships, legally, but I'm going to use the word meaning two or more people who are actively involved in the day-to-day running of the business.)
It takes only one person to form a corporation (you), and you can be its sole employee, too. This is sometimes a confusing point.
Most needlework teachers and designers who do not also have a shop or some other needlework enterprise are sole proprietors.
You may or may not have to file paperwork or pay fees for a partnership. Check with your state. If it is not required, I strongly advise you to see an attorney for a partnership agreement prior to starting your business. To save money, you can do it yourself with a book from Nolo Press or something similar, but you probably want to run it by a live attorney.
Beginning a corporation requires complex forms, filing fees, plus sizable attorney and accountant fees. There are also on-going paperwork and fees.
Why would any businessperson want to set up a corporation?
With a SP or a partnership, you are subject to unlimited -personal- liability.
This means if your business goes into debt, your creditors can seize your -personal- property. If someone sues you and your insurance coverage does not meet the amount of the liability claim, your personal assets may be taken and sold to complete payment. Pretty horrifying.
A person in an incorporated business technically has security from seizure of his personal assets. Only assets owned -by the corporation- may be attached to satisfy a claim. I said "technically" because this security - - called the "corporate veil" - - is being "pierced" more and more often nowadays. Don't opt for a corporate set-up because you think it offers 100% protection for your personal assets. It doesn't.
Now let me backtrack a bit to a limited liability company. This is a cross between a partnership and a corporation, offering the personal asset protection of a corporation but the flexibility of a partnership. These are fairly new legal entities, and if you are considering one of these as an alternative to a partnership, you definitely need to research the specific laws of your state. I will not discuss the LLC further here.
If you are a one-person operation, your options would be a SP or a corporation.
If you are in business with others, any of these legal forms would be a possibility, depending on whether the others are your employees or not.
Profits of a corporation are taxed at the corporate rate, which is usually lower, which is another reason to incorporate.
If you are a corporation, losses must be carried over to the next tax year. This is one downside to incorporating.
In a corporation, these taxes are shared by the corporation and the employee. Thus if you are the sole employee of your corporation, part of the tax is paid with "corporate" money and part is "taken out of your paycheck."
If you are a corporation, you do. 100% of these taxes must be paid by the corporation.
As a SP, your "pay" is technically called an "owner's draw" and is not deductible as a business expense.
Note: You are taxed on your -entire- profit from the SP, not just your draw.
The fact that you can't deduct your -own- pay is another reason people incorporate their businesses. You can, of course, deduct your employees' pay; and you can employ your family members. Check with your accountant for the ins and outs of this; certain conditions must be met to keep the IRS happy.
For a partnership, the same idea pertains as with a SP. The money you and your partner(s) receive is called a "partner's draw" or a "guaranteed payment." These are not deductible.
A partnership's employees' salaries -are- deductible, but that those employees can't be you or your partner(s)!
If your business is incorporated, the law considers the business a separate legal entity from you personally (which is why your personal assets are protected from a suit against the business). Therefore, the business can hire you as an employee; the business takes a corporate tax deduction for your salary, and taxes are paid with business money. You receive a W-2 at the end of the year and report your "pay" as you would any other salary (on the front side of Form 1040).
You may hire family members as employees in an incorporated business, too.
In a partnership, the situation is the same, except that the partnership agreement may spell out a mechanism by which the deceased partner's portion may be bought out by the other partner(s).
The corporation is different. It has a life of its own. A corporation may be dissolved -only- if the shareholders vote to do it. If one of the shareholders (owners) dies, his shares pass to his heirs.
The sole proprietor or the individual partner may set up a Keogh plan or a SEP-IRA, which are tax-deferred plans. (In a tax-deferred plan, you owe no tax on the money in the year you contribute it; you pay tax only when you withdraw it, presumably after your earning years - that is, retirement - when your personal tax rate drops because your earned income drops or disappears entirely. There is legislation afoot which would allow pre-tax contributions -and- tax-free withdrawals at retirement.)
These tax deferred plans are the equivalent to a corporate plan.
A cooperative can be either a partnership, a LLC, or a corporation. A cooperative, by definition, cannot be a SP.