* 2. place name of function in the placeholder in the lower left corner |
Thats the point! Just the name - no parentheses, no arguments!
What about the quicksheet I mentioned?

The help section about surface plots provides a link to the explanation of the CreateMesh() function just a few lines below the text you cited and again, if you follow that link and the information there is not clear enough, you are offered a link to the appropriate Quicksheet. This sheet deals mainly with parametric function but the syntax to use should be clear nonetheless with the information provided there.
Its the same in your German version as well. BTW, when using that German version you may encounter problems when using t as a quickplot variable or when dealing with Laplace transforms, as t will be interpreted as tonne and s as seconds. Thats very nasty and the only way out is to set (at least) the Math Language to English and its a good idea to switch the menu language as well.

You may also add the saddle and its tangential plane

For future questions please state which version of Mathcad you are using and its also much better to attach a worksheet rather than just a picture.
And of course - read the help thoroughly 