The way it works at the moment in the Multiplayer is that you place weapons on the map and when the round begins you go and collect what you want to use. This may change by the time it is released, but remember this will be the very first version of Multiplayer and there won't be any fancy spawn screens to select loadouts.
But in future I am sure that will be added, big plans for multiplayer.
Windows 7 Pro, Intel i7 3.8 GHz (Passmark: 9021), 16GB DDR3, NVIDIA GTX 780 4GB Superclocked (Passmark: 8056)