The user interface for CardioTrainer is smooth, though it may take a bit of time to fully get the ins and outs of the app. Luckily, the first time you open it, the app will lead you through setting up your workout days and times, as well as asking if you want to try any of the current free trials being offered.
The workout mode allows for several different types of activities that you can choose to do. When I was first using the app, I chose the walking option, as I was usually walking back and forth between my apartment and my friends', as well as just walking around my new neighborhood. There's also options like weight lifting, biking, running, skiing, and dancing.
For both the walking and running options, you can use your Android's GPS so that the app can track how far you've gone (you can change from miles to kilometers within settings), as well using your music player in order to play some tunes while working out. In the event that you happen to workout and don't have your phone, you can manually enter in your time and how many miles/minutes that you worked out.
From the main workout screen, you can now select the amount of time you want to workout, the distance you want to go (for walking, running, and biking), as well as a calorie goal for how many you want to lose.