In the yellow box, enter the text (in Tibetan script) that you'd like to see spelled out, e.g. བཀྲ་ཤིས་བདེ་ལེགས། Then hit return.
Since it is sometimes difficult to distinguish pre-initials from initials (if there is no vowel sign or stacked consonants), "འོག" may sometimes be added where it shouldn't.