In game character sheet

Hi,

I would like to make an in-game GUI that the player can refer to by pressing the "tab" key.
I have been searching around for this kind of functionality and can't find it for the life of me.

The GUI would have to do two things:

- Display during the simulation of the game without interrupting it(which I assume it would by default)
- Be able to display dynamic attributes relating to the player's character.

So, for example, John is playing the game, his character has a Strength attribute equal to 5 and an Intelligence attribute equal to 7, John would like to view his character's attributes and so presses "tab", which opens his character sheet, showing him the attributes and their values.

How would one approach this problem? (Also, know that I'm asking about the GUI, I don't expect you to tell me about making, structuring and effecting the character class)
I am not familiar with any GUIs that can be opened during a game, but then, I am pretty new to all this.

I would appreciate even just being pointed at cursory documentation on the subject.
Thank you all in advance.