To add the LevelEleven Score tab to the chatter layout, click on Setup in the upper right corner. Once there, click on Create and then on Apps. Halfway down the page, there is a table labelled Subtab Apps. This table has two options: Profile (Self) and Profile (Others). Both of these options will need to be edited. Once on the edit screen, select LevelEleven Score from the list on the left, and add it to the list on the right.