If you are not able to dictate in a text field, say "Show dictation box". Dictate your text in the box, then say "Transfer". The text will be pasted to wherever the cursor was when you opened the box.
The dictation box can also be useful in text fields where you are able to dictate, but perhaps you don't have full functionality. For example you might not be able to format or correct text. You will be able to do these functions by voice in the dictation box.