Quickcast will automatically target or trigger wherever your mouse is hovering.
Using standard keybindings, pressing Shift and a corresponding key (such as QWER for abilities and DF for Glyphs) allows for a Quickcast shortcut.
Quickcast Executed on Up:Edit
An alternative to the default Quickcast.
When enabled, all Quickcast actions will be executed when the key is released instead of when pressed. Players will see range indicators while holding the key down. You may cancel the Quickcast by pressing Escape or Right Mouse Button while the key is still pressed.
How to Enable or Disable Quickcast Executed on Up:Edit
1. At the front end interface (or in match) press Escape and click on Options.
2. Click on Controls.
3. You can enable or disable Quickcast Executed on Up here:
It's best to play around with what feels best in a Try Hero or Custom Game.