how do you make a stub in Eagle PCB software?

I am trying to create a stub in Eagle on the board design, but I do not know what function to click on in order for me to create a stub. I thought for a sec that Via's function would short the circuit, but not sure if this would work? Plus, wouldn't the shape of the stub have to matter? How would I perform an accurate 50 ohm stub? Im working at 2 GHz.

I guess the command will be ROUTE, WIRE, RECT OR POLYGON, depending how you want to draw the artwork. Eagle is a layout tool, it doesn't know about about transmission lines, impedances and such, but you can draw RF stuff as with any other basic layout tool. You need to calculate suitable 50 ohm line width beforehand, e.g. using Saturn tool kit.

Are you designing micro strip structures? Which substrate height? Open or shorted stub?

You mean radial stub? The trick is that this is an OPEN at DC, but a short at some RF frequenvy. The via is a short at any frequency down to DC, so this doesn't replace the radial stub.

I'm afraid there is no radial stub element in Eagle. You have to design dimensions using RF tools and then draw a polygon in Eagle.

I meant to say shorted stub, so I could just use the via's? Is radial stub an open stub, but in a radial direction?

Vias at the end of the line should be fine at 2GHz.

Yes, the radial stub provides a more wideband RF short than a rectangular quarter wavelength open ended stub
http://www.antennamagus.com/database...age.php?id=292

I am using Eagle and I want to short the end of stubs and there are only 3 different shapes for a via: circle, square, or octagonal. Which one should I pick to best fit an LNA at 2.4 GHz? Or will it not matter? the thickness of my board will only be 1 mm.

To create a stub you can make it in Board layout and use Rectangle design option (Board/Draw/Rect). Usually this is done on Top or Bottom layers.
The stub will be shown only in the board layout and not in the schematic.
The circle/square/octagonal is the shape of the pad of the via, and may not have importance which one you use. Circle is the most used one.