There is no strike action on 24 May.
The strike action is on 12, 13 and 31 May and 3 June.
The dispute has not been settled. It is now too late to stop this week's strikes, even if settled today, but no negotiations are known to be happening.
There are a number of posts on this forum detailing impacts.
Basically the whole of England is impacted with the exception of Merseyrail (for Liverpool area services) and the 'open access operators' (Lumo, Grand Central trains and Hull trains).
Wales and Scotland are not affected internally (although trains run by English operators will not run).
On strike days (except 13 May, which is a different Union) for instance there will be no service at all from Gatwick, and only services internally within Wales and from Wales to Birmingham, Cheltenham, Manchester, Crewe and Liverpool in England.
It will not be possible to reach London by train. To do so you would have to change to National Express Coaches at Cheltenham (in reality at Cardiff for more frequent service), Birmingham, Manchester or Liverpool.