The only way I get it to graph anything is to calculate the points tabularly to columns and then plot them e.g. as linegraph or scattergraph. I think it does not have a property to directly plot a function.
Although I do think that it has some kind of Visual Basic programming tools available, but I've never used that feature.
The quickest way to get your graph is to write your equation in a cell in column B like so,...=1/(A1^2+4) Where A1 points to the cell A1.
Then in cell A1 put in an initial value for x, say zero maybe.
In cell A2 put in the next increment of x, say 0.05 maybe.
Then select cells A1 and A2 together. Then put your mouse pointer on the little black cross at the lower right-hand side of cell A2 and drag it down to fill down the series in the A column. That will produce values of x that are incremented by 0.05.
Then select the formula in cell B1 and fill it down so that it automatically calculates the results for each x value. Then you can plot those columns in a graph.
If you understood how to do the above. Then you can get carried away with the values of x by simply experimenting with various formulae to define the values of x in the A column. In other words. define an initial value of x in cell A1. Then in cell A2 define a function that refers to cell A1 (the cell immediately above it). Then just fill down that formula. It will generate a new x based on the value of the previous x.
It's actually pretty slick once you get the hang of it. The original equation in column B will automatically update based on the new values in column A.