In my last Regency story, a reader commented that the idea of an entailed estate was new to him.
The beginning of understanding of the idea is to understand the inheritance of a title. It goes to the oldest son of the oldest son of the . . . oldest son of the man who earned the title.
As long as there is somebody in direct male descent of the person who earned the title, it goes on.
The title holder may have no living sons but a favorite nephew or grandson. The title, however, can go to some fourth cousin once removed whom the title-holder does not know or even dislikes.
If the original holder of the title has a lot of property, and seldom is a title given to someone who doesn't, then he can leave that property as an entailed estate so that it goes to the title-holder even if the title goes to the grandson of a second son.
Other entails were set up, however, for men who didn't have a title to leave with them.
The heroine's father in Pride and Prejudice had an entailed estate. Since he had only daughters, his heir was nearly a stranger.
Since the estate could not be removed from the line, it could not be sold. The current holder was only entitled to the income from this property. (And it could not be mortgaged, obviously.)
So far, this is what I know. I have some guesses, though.
I think this encouraged two very different sorts of property which are peculiarly English.
The one is farms. A great deal of English agriculture is (and more was in Regency days) on land which is owned by a major aristocrat, who rents it out to a farmer who hires a bunch of laborers to do the actual work. This has peculiar advantages to owners who can rent out property but not sell it.
Another is the peculiarly British government debt which is called a consol. This is a bond which is never redeemed but pays interest in perpetuity.
Now, consols were bought and sold by individuals back then; they even had a market price. Still, you can see the advantage to putting an entail into consols over putting it into a bond which came due in so many years. (Consols were invented from an entirely-different government need, I merely attribute the market for them until the British public took them for granted to the entails which found them attractive.)