To take full advantage of SketchUp's potential, you can install several extensions.
Teilweise kosten diese Erweiterungen (viel) Geld, doch es gibt auch kostenlose. Beachtet immer die Lizenzbedingungen, manche sind z.B. nur für Privatbenutzer kostenlos.
The easiest way to install extensions is via the built-in "Extension Warehouse" (which you can be found in "Window"). There you can find the extension "SketchUp STL", which is needed to im- and export *.stl files. Unfortunately, it is only possible to import single files, not several at once. However, this is a general SketchUp problem and is not limited to this file extension.
Attention: To install extensions over the Extension Warehouse, you need a free Trimble account!
However, not everything is available through the manager. A large platform for further extensions is called sketchUcation. Also here you need a free account.
As already mentioned, I can recommend the following extensions, which can also be downloaded from sketchUcation: Fredo6 JointPushPull & Fredo6 Round Corner.
You also need the library "LibFredo6" to make the other tools from the author work.
The *.rbz files are installed via "Extension Manager". Simply select the file and "Activate" if necessary. Videos about the functions can be found on the corresponding website.
Do you have any useful extensions or would you like to know more about SketchUp? Why don't you leave me a comment?