How can i add a condition value to another box

Click on Conditions, then choose "Update a Form Field Value" option:

Then set a condition like this:

If you input in Text Box 1 the number 10, then you output that value to Text Box 2, how? Simple click on Add Field button, and select the variable that correspond to "Text Box 1" field:

Please try this simple example here: http://form.jotform.co/form/43107308046851

You might want to see guides related to apply conditional logic on a form:

http://www.jotform.com/help/268-How-to-Insert-Text-or-Mathematical-Calculation-into-a-field-using-a-Condition

http://www.jotform.com/help/57-Smart-Forms-Using-Conditional-Logic