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'"
Execute the launch command in a subprocess

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'