1.first you need to follow the instruction as shown in below link
https://github.com/IntelRealSense/realsense-ros/tree/ros1-legacy
2. after doing it you've to run the ddrone.py
You can either launch your launch file separately on another terminal or you can make changes in code to add a command for running launch file as shown below.
# Define your launch command launch_command = "roslaunch realsense2_camera rs_camera.launch enable_gyro:=true enable_accel:=true unite_imu_method:='copy'"
subprocess.Popen(launch_command, shell=True)
Below is the command you've to run if you are not getting IMU data after following the above link.
roslaunch realsense2_camera rs_camera.launch enable_gyro:=true enable_accel:=true unite_imu_method:='copy'