The two tools from left to right are:
* Draw an AOI by clicking each point and double clicking to complete
* Draw an AOI by freehand sketch - hold down the mouse and sketch
If the dataset you are viewing/downloading is a public dataset then you can draw your AOI anywhere you like.
If you are a registered user viewing/downloading a restricted dataset, then any AOI you upload, or draw, will be clipped (restricted) to your default AOI as shown below as that is the area you have been authorised to download restricted data for.
Cards on table? I'm new to any and all of this. All I want is an accurate height map (DTM?), the boundaries of which are set by map coordinates (for example: -5.618300,50.223772,-5.379607,50.071058). My ultimate goal may seem frivolous, but I want to convert this data into a .png/.raw image, so I can use it as a base map for the game 'Cities:Skylines'. Any help greatly appreciated.
Please refer to the blogs and help guides on Environment Agency Geomatics Hub (arcgis.com) https://experience.arcgis.com/experience/753ad2ebd3554fa696885b8c366c3049/page/page_10/ which contains some basic getting started with LIDAR help.
You will need to download the data first from the DSP (you can upload a shapefile AOI of the map coordinates or search) and then download the data (I would download the 1m 2019 LIDAR Composite DSM data as a surface model would be more applicable for gaming than a terrain model) and put it into a GIS such as QGIS to convert into latitude and longitude (the example provided is in lat/long but our LIDAR is in OSGB projected coordinate system)