How do I navigate through timeline?

You've got multiple way of selecting a specific frame.

What does ShiftX / ShiftY means? What is X / Y?

The SFV engine has two main ways of moving a character: 1) by using forces (gravity, impulse) 2) using position shifts. On the top right, you can see all shift categories. The main ones are:

How do I know which hurtbox has which property?

You can select each box by clicking on the timeline element. I know it's not ultra convenient but it works.

What does those icon means in the hit/hurtbox timeline?

Projectile: ★. Strike: 🤜. Throw: 🖐.

There are things I still don't understand.

The SFV engine is complex, not much I can do without going in full details. Please don't hesitate to ping me on twitter or on reddit.