if you right click it freezes the prop (when you freeze it, let go of left click). What this can do is if you left click and hold u can pick up and move a prop (item) around. This is known as the phys_gun or the Physics gun. So you should have your health in the bottom left, and you should notice that you have this weird looking blue gun in your hands. I have a statistics bar in the bottom right hand of my screen, ignore that. Now this above is what you should have on your screen, if you loaded the map called gmod_construct which is the default map with Garry's Mod. (have in mind I have a lot of addons that you will not recognize from props, tools, and vehicles, to entities and npcs)

Okay first load up a level like explained in the Introduciton and pull up the Q menu. Now that you've read through the introduction for the basic boring information, now it's time to move onto the fun part explaining the tools you have at your disposal to build some crazy contraptions like rides and houses, to reeking havock with lasers and explosions.

How to pick up guns in gmod