With elliptic curve crypto you don’t encrypt directly with the private key (just a number) or the public key (just an x,y point).

Instead we usually multiply our private key by someone else’s public key to get a point.

We take that points x value, hash it and use the output as a symmetric key.

The other person can take our public key and multiply it by their private key to get the same point.

We end up with something like this:

OurPrivate * TheirPub == secret point.

(TheirPub is actually equal to TheirPrivateG, thus the secret point is really OurPrivateTheirPrivate*G)