Manual backup is satisfying and easy to do. When you have the database selected in DT, go to File>Export>Database Archive. It will create a zipped folder of the database that you can store on your backup system of choice (I have an external drive for this purpose, and date the zips).
Time Machine is more annoying and I will leave you to figure that one out! But I will let you know that there is a good little app called TimeMachineEditor which lets you run Time Machine manually if you don’t want it running all the time (e.g. if you’re on a laptop and would prefer not to have your external drive plugged in continually).