The directional particle へ could be said to be a more literary version of the target particle に when the particle is used to denote a direction of movement. It is often considered a slightly more literary or formal version of the target particle に when denoting a direction of movement. While に is much more common in everyday speech, you will still hear へ in conversation, and it appears frequently in the JLPT examinations from N5 onwards.
学校に 行きます。
I will go to school.
学校へ 行きます。
I will go to school.
Just like the topic particle は is pronounced wa, the directional particle へ has a special pronunciation. When used as a particle, it is pronounced e (eh), not he.
友達に 手紙を 送ります。
I will send a letter to my friend.
友達へ 手紙を 送ります。
I will send a letter to my friend.
Nor does the direction of movement need to be physical.
【A】から 【B】に 変ります。
To change from A to B.
【A】から 【B】へ 変ります。
To change from A to B.
The へ particle cannot, however, be used to mark an objective, as a location marker, or as a time marker.
友達へ 会います。(✘)
友達に 会います。(✔)
I will meet my friend.
本は ボックスの 中へ 入っています。(✘)
本は ボックスの 中に 入っています。(✔)
The book is inside the box.
４時へ 家を 出ます。(✘)
４時に 家を 出ます。(✔)
I’ll leave the house at 4 o’clock.
While に and へ are often interchangeable for travel, へ is exclusively used as the salutation at the beginning of a letter or email, translating to “Dear…” or “To…”