Students can use the onscreen/virtual keyboard (sometimes referred to as 'formula editor') to enter answers. Specific functions, like, log and ln, can be found on the tab 'function'.
Another way of entering answers is using your own keyboard. This way, you can also type functions, for example you can simply type 'ln' or 'log(a,b)' for log_a(b).
This is all explained in the page "Getting used to the test software" in the "OMPT // Welcome" chapter.