Use a saddle if the ghast is rideable in your game mode or mod
Approach the ghast carefully and mount it with the interact key
Control movement with the standard movement keys or controller input
Use a lead, harness, or special riding item if required by the mod
Keep altitude steady to avoid falling off
Dismount with the standard dismount key
If the ghast is hostile or unrideable in your version, use a mod or custom command that enables riding