There are options in the View menu to display proteins in different ways. Normally the Cartoon view is used but somehow your puzzle is showing the Stick view. I just checked and Tutorial Puzzles don't show the View menu for you to change the view. This must be a bug.

You may want to reset the puzzle or close foldit and restart to see if it fixes the problem. If not you may still be able to play the puzzle since it's only one of the many ways to view proteins. Please let us know what happens.

Right,when I play intro puzzles I couldn't see view menu,and so I counldn't change.Then I check science puzzles,I can find view menu and am able to use cartoon view.But every time I use rubber band it go back to stick view and I have to set again.

The next time you have problems like this,
you could share a screen shot to Global Chat
and ask how to fix it. You can share screen shots
using the camera icon next to the Send button
in Global Chat.

A screenshot was shared in Global Chat and I posted a response. The puzzle was level 5-1: Quest to the native and it was in Stick view.

There are hot key combinations that will change the protein to Stick view. They are listed in the Help menu in the science puzzles (scroll down).

Ctrl-Shift-M is one of the combinations that switches back to Cartoon view. I can't remember them all, & I just shut down my client.

If you use Ctrl-Shift-click & drag to create bands, is it possible you are pushing a letter key that is triggering one of the hotkey View combinations?