Assuming you mean owning a share in a master limited partnership (MLP)as an investor, he short answer is: you get tax-deferred income on a quarterly basis, and pay income tax on your share of partnership income, which is usually far smaller than the distribution.
The long anwer: the important thing about an MLP, or any partnership, is pass-through taxation. That is, an MLP does not pay an entity level tax the way a corporation does. Rather, the partners--that is you and the other unitholders--are allocated their proportionate shares of all tax items, net them out, and pay the tax on the resulting taxable income. So, you will be allocated a share of the partnership's income, its depreciation deductions, etc. All this is on paper--you don't actually receive an amount equal to your share of income.
You do, however, receive a quarterly distribution, which is like a dividend, except that it is treated differently for tax purposes. Because the partnership doesn't pay a tax, it can pay out more of its income to you in case than a corporation typically can. Instead of being taxed currently, the distribution is subtracted from your basis in your partnership units. When you sell your units, your taxable gain is the difference between your sales price and your adjusted basis, so the tax on the distributions is collected then. While the distributions lower your basis, your share of taxable income and other things increase it, and so it takes longer than you might think to get your basis to zero. If you ever do get to zero, the distributions would become taxable.
For more information, visit the website of the MLPs' trade association, the National Association of Publicly Traded Partnerships (http://www.naptp.org)...the answer is being submitted by its executive director.