Copy of:
https://forums.frontier.co.uk/showthread.php/370855-Neutron-Stars?p=5827274#post5827274
Bit more tailored to how to use the highway rather than how to neutron supercharge but others have explained that:
Guess I can field this one having used this extensively in recent times:
There are 3 Neutron stars in the bubble (at least to my knowledge). There's Beta Sculptoris, Jackson's Lighthouse and eta cassiopeiae.
The Neutron highway is for explorers and only really starts a few thousand LY North of the bubble.
https://forums.frontier.co.uk/showthread.php?t=163816
Short answer is go to the co-ordinates listed in that thread or the system name given for it's centre and use Khaos526's advice about filtering the map. You should see a veritable "field" of neutrons and black holes. Pan around left/right/front/back/up/down and eventually you'll reach an "edge". There are many neutrons around that are not in the field but the fields are obviously good for well aligned jumps in the direction you want to go in and consistently hitting neutrons.
The "highway" is the term given to using the neutron stars as fast travel between 2 points, the common ones are Sol->Sag A*, Sol->Beagle Point and Sol-> Colonia
https://forums.frontier.co.uk/showthread.php/281825-2-2-Building-the-Neutron-Highway-Grid
As in the above thread there is a plotter tool that will try and route you via neutron stars:
https://www.spansh.co.uk/
This is fantastic but works using EDSM so only routes you via neutrons that are recorded into EDSM, there may be a more optimum route it misses because it doesn't know. It works more than fine for the average traveller looking for a boost but isn't great for people like the Buckyball racers.
Neutron stars damage your FSD so you will want an AFMU as otherwise it'll malfunction below 80% module health. Neutrons also require manual plotting on the galaxy map each jump. This means if you can copy/paste in from Spansh or elsewhere you can plot fairly quickly, if not you are panning around looking for a suitable next jump.
The latter takes a long time, even with the neutron stars giving +300% to your range (400% total) it won't boost you too much because of the sheer amount of time finding a suitable system will take. It will save some time but not be incredible.
On the other hand if you have a copy/paste route it can lead to insane speed. I recently did Sol->Sag A*->Beagle point. 2h 25m to Sag A* and a further 4h 10m to Beagle for a total Sol-BP time of 6h 35m. Average 10Kly/hr. To do that I started with Spansh and then manually flew the route 3 times editing it with all the neutrons that I could see that Spansh didn't know about.