Hi Ian.
Drone Scene, with its switchable layers and loads of site recommendations, is your friend.
But it can be confusing.
The Class D airspace layer covers a lot of real estate but isn’t that relevant to us. Turn it off.
Parks, prisons, hospitals and other sensitive areas will show as irregular yellow patches. Use your judgement - flying in parks without annoying people should be fine - if there is no local by-law in place. Often there isn’t but “No Drone” signs are displayed. Probably best to obey them until you have enough confidence in the law to tell the parkie to ___ off.
Hospitals, pretty much a no for the patients’ sake. Prisons - your drone may be confiscated and you may have an enforced holiday
Purple markings, mainly on coastlines and waterways. Crown Estates land. They have a fair attitude to drones being flown from and over their land - follow the drone code and you will be ok.
Not so Forestry Commission and National Trust / English Heritage. They do not allow take off or landing on their land. They also claim, wrongly, that you cannot overfly. So most people take off from a public footpath or roadway close to the property boundary and overfly at a height that doesn’t attract attention - 50 metres or so.
You can fly in a Flight Restriction Zone but only with prior permission. Leave them alone for the time being.
Blue circles may appear on the map where there were no marks a couple of days before. These are temporary exclusions, sent out as a NOTice to AirMen (NOTAM). As with any of the other markings on the map click it and an explanation will popup.
The green tabs on the map are sites that a member of the forum has flown. Ideally they will have given some useful information such as who to contact if permission is needed, where to park, where to take off, any hazards, any other interesting things nearby and nearest pub/cafe/public toilets 
If using the magnifying glass (top right) to start a search doesn’t bring the results you want eel free to keep asking questions, we have a whole category devoted to them: #questions-and-answers
Happy flying!