I was using the libre office maths for the first time and i m not able to create the formula please help me out
Which one? Math is a markup language so you need to describe what you want in the editor (right lower pane). For example, type nroot {3} {(x^2 + y^2)} and see what you get in the upper panel. The left panel allows access to the markup elements of math. At least read chapter 1 of the LibreOffice Math Guide
A hint: if you want to insert a Math formula into a Writer text document, simply type in the respective code such as (a + b^2) over (c^3 - d^3), select it, then Insert → Object → Formula from the menu.