A paper template makes you do the arithmetic, and the arithmetic is where logs go wrong. I built this so you type the trips and the page keeps the running total at the right rate for each date.
Each row needs the same five things: the date, where you started, where you ended, why you went, and how far. Those are the fields the IRS lists for a mileage record, and HMRC asks for the same in practice. Add the vehicle if you drive more than one.
How to fill it in
Write the entry the same day if you can. A log made at the time of the trip is easier to defend than one rebuilt in April from a calendar.
Put the business reason in plain words: "Install visit, Delgado kitchen" beats "work". Use the lookup button for the driving distance if you do not know it, or type the figure from your odometer.
When the year ends, download the PDF, sign it, and keep it with your tax records. The page shows the rate it used so you or your accountant can check it.