Good start - keep it up. All v. useful additions.

May I suggest the historic=castle tag for this?
osm.wiki/Tag:historic%3Dcastle

You haven't tagged these (presumably) buildings, so OSM doesn't really know what they are. As far as OSM's concerned they're just generic areas.
You need to select the areas and then choose a tag from the menu on the left hand side of the screen.

Here's a neat trick: when you've got an area selected, hit "s" and it will perfectly square-up the edges for you.

What route is this? Is it an official designated route? There are ways of adding these but they may require a more powerful editor.
If it's a personal cycle route, OSM isn't really meant for this sort of thing (any more than Wikipedia isn't meant for personal essays).

You haven't added any tags to these lines, so OSM doesn't "know" what they are. They could be fences, rivers, train lines, anything. They also go over existing roads, so I'm not sure what you're trying to add here.

Hi, I've made a small fix to this edit by connecting the ends of the steps you created to the roads they appear to run on to. It's important to actually *connect* these ways in places where they are traversable across, otherwise tools that use OSM data don't know they are connected and can't e.g. route across them. In the web editor (iD), nodes should feel like they magnetically "snap" together when they're connected.
Keep it up - cut-throughs like this are extremely useful features to add.

Nice addition - I removed the superfluous "point" Whiteheath Junior School because we have a general guideline we call "One feature, one OSM element". Read more here: osm.wiki/One_feature,_one_OSM_element
Happy mapping.

Oops looks like a bit of your way combining (?) might have given roads around here an ugly (semicolon separated) name and some ugly attributes breaking some OS Locator matches e.g. http://ris.dev.openstreetmap.org/oslmusicalchairs/map?osl_id=559309

Don't be discouraged - everyone makes mistakes on their first edits.

Please don't give things "descriptive" "name"s. The "name" tag is intended for specific names of objects.
osm.wiki/Key:name
There are special tags to denote things as e.g. allotments. Even "surface" tags that you can use to notate the surface of a pitch
osm.wiki/Key:surface
I've fixed a bunch of things here for you now.

Tip: if you use a non-Internet Explorer browser, you can use the slightly easier editor iD.

Here, you could have removed the "indian restaurant" tagging without removing the entire node (that contains really useful address (housenumber) data - presumably the address is still there it hasn't got up and walked away).
I've restored this now for you (without the restaurant).

I've reverted this.

This isn't really the intention of OpenStreetMap. OSM is a shared, globally edited map. It's a bit like wikipedia for maps. Editing the map edits it for everyone - it's not really intended for personal notes.

What *would* be useful however would be to add some of the house numbers and addresses in this area :D

Oh and there's also a specific "retail building" tag. I've switched the commercial building to that too.

Try not to use general descriptions for "name"s. The "name" tag is meant more for specific names of objects. I've removed some of these and added a specific parking tag to your parking area.

Ok, I've pulled the border of the school back from the path then so it's clear.
Keep up the good work - footway/cut-thoughs are extremely useful things to add.

Yeah sometimes ground truth is the only way to know. If there aren't any signs, can always find out the addresses of nearby premises.

The "station" object you moved is supposed to mark the position on the track (in this case, underground) that the platform(s) are. The entrances to the tube are marked using different objects, such as osm.org/node/1678155316

I've reverted this changeset with my changeset
osm.org/changeset/28662734
but then restored your sainsburys repositioning in
osm.org/changeset/28662792

If you need to travel through the school grounds to traverse this footway, it might be good to set the end nodes as "gate"s so pedestrian routers don't try to send people through the school as a shortcut.

Great start - as you can see plenty of road names are missing in this area.

p.s. if you use a non-Internet Explorer browser, you'll be able to use a slightly easier editor, iD.