Is your input axis really called “horizntal”? I bet it’s “Horizontal”. And your “vertical” axis is probably “Vertical” too. And 0.0 should be 0.0f because it’s a floating point number.
Every detail matters. You are missing a ‘f’ at the end of 0.0 on line 7. The forces the value to be a float. By decimal numbers without a specifier (numbers like 0.0 or 3.14) are doubles in C#. But everything in Unity takes floats. The ‘f’ casts the number to a float.
On line 8, ‘Rigidbody’ should be ‘rigidbody’. Rigidbody with an upper case ‘R’ refers to the class. ‘rigidbody’ with a lower case ‘r’ is the specific instance of that class on this game object. This kind of naming is used frequently in Unity: Collider the class, and collider the specific collider on this game object, or Transform the class and transform the specific instance of the transform on this game object.
And finally your are missing a ‘}’ at the bottom of the file…may just be a paste error.
Edit: And @tanoshimi is right horizontal and vertical should have upper case ‘V’ and ‘H’ unless you’ve renamed the axes in the projects settings (though this would generate a runtime error, not a compile time error).