All you need to do in desktop is left click. Nothing more, nothing less.
As for More Controls:
- Holding RMB grabs objects.
- Pressing LMB while holding an object levels it to it’s nearest axis.
- T opens your radial menu.
- R Is secondary, for stuff like selecting objects with the dev tooltip.
- Holding E while grabbing on object allows you to rotate it, like in Garry’s Mod.
- Holding Shift+E while grabbing an object rotates it horizontally.
- Shift + Scroll wheel will scale held objects.
- If scaling is enabled in your radial menu, CTRL + scroll wheel scales you.