Welcome to NanoBricks; there are 3 easy steps to start building nanostructures:
When you begin, you'll already be using the Pointer tool, which you can use to place voxels; click to place, shift-click to delete, or hold alt and move the mouse to paint. Drag the mouse to look around (orbit). Instructions for using the tool show up in a blue box to the top left, right under the toolbar.
If you don't want to draw, you can also import files from another 3D modeling program, using the Import button in the main toolbar. Follow the instructions in the top left.
Click the "Voxels > Strands" button in the toolbar to generate strands from your voxel design; you should see a bunch of blue and black lines appear---those are your strands. You can toggle the Voxels view off from the "Views" pane on the right in order to see your strands better.
Click the "Sequences" button in the toolbar to open the sequences window. Choose "Random" from the dropdown. Click "Generate & Thread;" you should see a bunch of sequences.
You're done! Now you can...