Every cell needs a symbol. Symbols allow one to instantiate them in the higher level schematics and make them more readable.
1. From the Create menu in the schematic window, select Cell view -> From Cell view
A pop-up window will appear. Make sure that Cell Name should be same as the schematic name. Then click OK.
We will see Symbol Generation Options, which is for specifying location of the pins in the symbol. We can keep the default of pins location or change them.
After selecting pins and clicking OK, a Symbol Editor window will show up as follows:
We are able to use this symbol in our design. But we must create a more meaningful symbol. For an inverter, it should look something like shown below. How do you get to that symbol view? Use a menu circled in the window. There you have options to draw triangles, squares, and rectangles and manipulate the geometry of your symbols. It is a good practice to make all your symbols of standard cells of the same size.