I like to look at it in terms of Energy.

If the Earth started a very long way away from the Sun ('infinity') and fell in towards it on a direct path, it would gain a certain amount of Kinetic energy (i.e. be going at a certain speed) by the time it arrived at our present distance due to it accelerating all the time it was approaching the Sun. That amount of energy is called its Gravitational Potential Energy - it is the work which is available from bringing the Earth from infinity to its orbital position. (It isn't 'quite' at the bottom of gravity well - it's 150 million km away from it)

If you could then make it 'turn sharp left', so its motion was tangential, it would go into a circular orbit- attracted to the centre but going just fast enough not to fall or to escape. Its Kinetic Energy would be exactly the same as its GPE. That's the situation for every orbit. The potential energy would be the same amount (but negative, because we got work out of the process of falling) as the KE. Its total energy would be zero.

If it didn't quite turn hard left - went off at a different angle - then its orbit would be an ellipse (which, of course, it is). The total amount of energy would still always be zero but when it was further away it would be going slower (less KE) and its PE would be less negative - still adding up to zero and vice versa when it was closer.

Rambling and confusing but interesting - total energy = zero!!