What is different between tow words :
Hierhin und Hierher
Hallo 😀. Very good question. There isn't really a big difference in spoken German, both are used when expressing a movement towards a place. The only difference is the focus.
Hierhin has focus on the final direction. Hierher has focus on the starting place.
Er kommt hierher <-- he leaves a place to come here (er verlässt einen anderen Platz um hierhin zu kommen) Er kommt hierhin <-- he just comes towards here.
This is generally how it works but hin und her are quite flexible and the differences are very small.
In other scenarios outside of the hier-, her would express a movement towards the point of the view of the speaker whereas hin would express the movement away from the point of view of the speaker.