Need help with inventory system:

I have only had about 2 - 3 weeks of experience of coding so it would be nice to have some help with this. How would I code something as complex as a GUI inventory system for the player? How can i get it to where if he clicks on a item on the ground that item appears in his inventory? Then how can I get it to where he can take an item in his inventory and hold it in his hand? Even more importantly, How would i get it to where each weapon has a specified amount of damage it can do, and then when it strikes an entity, it deals that exact amount of damage. The weapons and targets use the collision system to know when the target was hit. Each target has a value: = 100;
This specifies the amount of health points the target has. In this case it has 100 Hp.
In the game the Player is a camera (using the playcanvas “first_person_movement” script.). The player has a model attatched to it called the “hand”. when the player selects a weapon to hold, the hand’s model changes to that weapon.

you can take a look at ‘Going Around’ project, i am still working on inventory too so i still can’t be of much help