Barista trainer isn’t really a promotion in the sense you will get a higher wage. As a barista trainer you learn how to train new partners using the barista basics as a guide. For each person you train its like a 70 dollar bonus (may very based on location not sure). You will watch some modules and your manager may talk to you about how you can be a good trainer before you train someone. To be honest the most important part of being a barista trainer is it puts you a step closer to becoming a shift. Also you will be expected to help train the new partners and coach them no matter who their actual trainer is after the first week. After all learning the job takes months and trainers know how to coach new partners better than standard baristas.