Since the basic control of the game is not obvious, so I hope this guide can be of help.
Basic Control
About Potion
Player will have 4 Potion slots to use, each can hold 5 Bottle for the total of 20 bottles.
You can swap potion slot by pressing [2] on your keyboard.
This also apply to weapons as well, you can equip and swap between 2 weapons by pressing [1]
Potion have two grade in total, the small one cost 7 souls for each and the big one cost you a whooping 30 souls. So use it wisely.
Thanks to OnTour for his great guide, all credit to his effort. you can also read the original guide from Steam Community. enjoy the game.