Normally when you do not have a keyboard what you use to write is the touchpad of the mobile or if you are on the PC the on-screen keyboard that offers you Windows, however, there are other ways to write in a more efficient way.
For that, there is an application called speech notes. If you are from a PC you can use it from your browser by going to the https://speechnotes.co/ page. On that page, you only have to click on the microphone icon at the top right and when it appears along with a red dot speak and everything you say will be written in the text field of the central part.
The application works very well because it works with a Google spelling checker API so the words that other speech recognition programs normally do not understand correctly can interpret and write it correctly.
This app is also available for Android which can be downloaded from the Google Play Store. You can download it to your Android from here.
Alternative for voice speaking without the keyboard
An alternative to the previous application exists a call Dragon NaturallySpeaking for Windows and for Android it is known by the name of Dragon Mobile Assistant which does work very similar to Siri of iOS and so far it is free.
The difference of this is that for Windows is paid and not as accurate as the first since it apparently does not work with a Google API. However, this app on Android is usually very useful and worth a try.
You can download it on your Android from here