Blender is probably the best free solution to create 3d models. If you want to take a few screenshots in Blender, here’s how
1. Either use the keyboard and hit the button “PrtScn” or
2. Click on File, then DUMP 3D View or
3. Click on File, then DUMP Screen
All 3 methods should work to take screenshots in Blender. If you want to create a “real” render of your models, you should read the Blender manual. Rendering is how you would normally take pictures of your models.
Watch this Blender Youtube video to get a clue: