To assign a style to one or more cells, select the cells and then choose the desired style name from the Style submenu.
The cell styles listed in the Style submenu are defined in the stylesheet assigned to your current notebook. Mathematica assigns a default stylesheet called Default to new notebooks.
Styles can also be assigned to individual words or characters.
The Other dialog box lets you type in a style name to be assigned to the selected cell or text. Not all styles defined in a stylesheet need to be listed in the Style menu. You can also assign cell options by typing the option setting in this dialog box.