Lost my first reply. Here's a 2nd attempt:-

No, it's a mistake. I added it because EveryDoor showed no gates at all in that area. I would have added the other 2 nearby ones, but didn't have their exact locations.
After some investigation I've found they're defined as wicket gates, as opposed to gates. Not my idea of a wicket gate, but the english language is notoriously imprecise. EveryDoor seems to completely ignore wicket gates - I'll get in touch with the developer. But I also notice some other software does the same e.g. OrganicMaps (I forget where I first noticed this behaviour).

Thanks.
Is there anywhere I can learn how to fix things myself?

Hi. If I remember correctly, there's a double gate across the track, as I added, but when I moved position (a short while later) I could then see a short section of fence behind the north gatepost at right angles to the gates (roughly west-east). In the middle of the fence is a stile. I almost certainly positioned this carefully, but it looks like EveryDoor has snapped it to the track.

Looks fine. Thanks.

The gate is in the boundary railings (& hedge). The path continues from SE to NW out of the park and into Regent Park Avenue as steps (up), but I don't know how to add this.

Thanks. Think I've fixed those now.

No, they're to the side, but right at the very edge of the road or pavement.
11132855327 to the canal (SE) side;
11132853547 to the east side. There are also steps down the side of the bridge (N-S) from this stile to the tow path, but I've no idea how to add these.
Not sure why Every Door is doing this. I definitely did not position them touching the road (after last time).
I've had a look at correcting both of these in the ID editor, but can't see any way of doing it. Would you be able to correct them for me, or point me in the right direction? TIA.

Not sure how those have happened. I've tried to move them.
11100300210 by the road side, at the top of the steps.
11100291768 next to the road.

Thanks. Thought it was odd that the trig point was 'missing'. Strictly it's a gate next to a stile.
I think it's a problem with apps using out-of-date underlying tiles.

Thanks.
Probably no. 6, but I'll check (probably next week, now).
I find I make quite a few (silly) mistakes with StreetComplete. Usually I make a mental note to fix them later.