Just go to the directory where that launchfile is placed.
For example it is in /home/workspace/myros/launchfiles, go with cd to that directory (cd /home/workspace/myros/launchfiles) and then start the launchfile with
roslaunch myexamplefile.launch
Here is an example file which works with a sick s300 laserscanner and hector mapping without odometry:
<launch>
<node name="laser" pkg="cob_sick_s300" type="cob_sick_s300" respawn="false" output="screen" />
<node pkg="tf" type="static_transform_publisher" name="odom_to_base_lnk" args="0 0 0 0 0 0 /odom /base_link 100"/>
<node pkg="tf" type="static_transform_publisher" name="base_lnk_to_laser_lnk" args="0 0 0 0 0 0 /base_link /camera_link 100"/>
<param name="pub_map_odom_transform" value="true"/>
<param name="map_frame" value="map" />
<param name="base_frame" value="base_link" />
<param name="odom_frame" value="base_link" />
<node pkg="hector_mapping" type="hector_mapping" name="hector_mapping" output="screen">
<param name="use_tf_scan_transformation" value="true"/>
<param name="use_tf_pose_start_estimate" value="false"/>
<param name="map_resolution" value="0.050"/>
<param name="map_size" value="2048"/>
<param name="map_start_x" value="0.5"/>
<param name="map_start_y" value="0.5" />
<param name="map_multi_res_levels" value="3" />
<param name="update_factor_free" value="0.4"/>
<param name="update_factor_occupied" value="0.9" />
<param name="map_update_distance_thresh" value="0.04"/>
<param name="map_update_angle_thresh" value="0.006" />
<param name="advertise_map_service" value="true"/>
<param name="scan_subscriber_queue_size" value="5"/>
<param name="scan_topic" value="laser/scan"/>
<param name="tf_map_scanmatch_transform_frame_name" value="scanmatcher_frame" />
</node>
</launch>