@vivi yeah see you've got an index on the bottom and an index on the top. Bottom one should be something like i = 0 or x = 1, and top one will either be another number like 6 or 100, or it might be infinity oo. What you do is you add together all the terms inside the sigma, substituting in the letter or variable acting as the index for each number between the top and bottom inclusive. For example, if you had (\Sigma_{i=0}^5 x), this would be 0 + 1 + 2 + 3 + 4 + 5, which equals you licking my balls.