I have saw the sidebar marked in the picture enabled in other people. How can I enable this for me?
EDIT: The bar doesn't appear at all, I mean, the "-" sign of the show/hide options doesn't appear. How can I make show this?
See the little "-" sign in the top part of the circle in your screenshot? When you do a Google search, it'll be a "+" when the results are first returned. Click the + and it expands to the side bar you're talking about.
Click "Web [+] Show options..."
If that doesn't work, switch locals to en-US or en-GB (If you prefer English...)
Google have a habit of gradually rolling out features to different locations. If you aren't seeing show or hide on the results page then Google probably haven't decided to give you that feature.
I found the answer.
You need to go to the option Interface Language and set it to English.