Formatting a paper in MLA format means making sure that your paper is typed, double-spaced, with one-inch margins. You should always make sure to use a legible font. Times New Roman and Courier are approved fonts, but you should always follow your teacher or professor's instructions as to which font to use.
On the first page of your paper, you should use a heading in the upper left-hand corner. This heading should list your name, the instructor's name, the course name, and the date. The heading should be double-spaced, just like the rest of the paper. The title of your paper should be centered on the first line after the heading. You should have a header with your last name and the page number in the upper right-hand corner of each page.
Some instructors ask for a cover page instead of the heading, so be sure to consult your assignment for instructions.
This is basic information about MLA format. For more detail, you should refer to chapter four of the current MLA Handbook or an online writing lab such as the Purdue OWL.