If you are new to Sufferlandria or new to smart trainers, you may find that on your first ride it feels like the trainer isn't properly applying resistance. There are a few things that you can check to troubleshoot this issue.
If you are connecting your smart trainer using an ANT+ connection, you will be presented with two options; "Bike Power" and "FE-C". If you select "Bike Power" the app will be able to read your power but will not change the resistance as you ride. You will need to select the "FE-C" connection so that you have the option to ride in either ERG or Level mode.
When you first start using the app, all of the workout targets will be based on percentages of your FTP (and later 4DP once you do Full Frontal). If you feel that you aren't getting any resistance from your smart trainer your FTP might be set too low for you and subsequently, your power targets are going to be too low as they are a percentage of that number. When this happens, you won't feel much, if any, resistance from the trainer.
You will need to head into your Settings and increase your FTP. Usually, a setting of between 150 and 200 watts is sufficient to feel the resistance. If you are using the desktop app, you will also need to enter a LTHR in order to save the changes to your FTP. If you don't know yours, you can enter 90% of your max HR as an estimate. You can always adjust your FTP further if you find that workouts are still too easy, or conversely, too difficult. Be sure to adjust not only FTP, but all of your 4DP settings. For more details on how to do this: How To Edit Your 4DP.
Ideally, you will take the Full Frontal test (in level mode, NOT ERG!) in the coming weeks to get your 4-dimensional power profile. Once you do that, all of your workouts will be customized to your abilities!
If you need further help, please submit a help request here.