Is this sentence corrent correct?

Counter that compute things bought in supermarket.
A counter that computes things bought in a supermarket.

Missing a couple articles (a/an/the).  You have to keep an eye out for those, they're tough to know but for a native speaker it sounds really awkward when they're not there.  You might consider changing 'that' to 'which' though it's not necessary.  Just a suggestion as it seems to be more proper to the way you're describing something.

For simple questions like this, you might try the Answers category rather than Notebook.  At answers you can ask a question like that, and people usually get to them more quickly there.  In their notebooks, most people practice their writing, especially longer texts.  It's okay here too, of course, it just might be faster in Answers if it's just one sentence you want checked.  Good luck!