We see that a few of you are having trouble navigating the UI in order to access weapons and set loadouts. Here is a short pictorial to help you.
Under the 'Armory' tab, click on Operative.
Next, click on the Operative you wish to use and then select Weapon
You can either click on the gear icon beside the weapon that's already equipped OR you can click on the weapon tile to open up the armory. From here you can also edit each individual weapon by clicking on the gear icon. Finally, select 'Equip' and you're all done!