The Portraiture gives you an overview about your character. As the ingame-describtion already states, you see your portrait and your belongings. Therefore the portrait shows you your appearance currently activated raiment, your satchel and current active spells, your activated Black Rite and the amount of Lacrima in your property.
When entering the Appearance-Menu, you have 4 different menu options, allowing you to change details concerning the character appearance.
Entering this menu gives you the option to change the gender of your character. This change can be done at no cost any time in the game.
Entering this menu allows you to change the details of your characters head. You can change the actual face (24), the skin color (15), the hair style (15) and the hair color (12).
In this menu you can change the Raiment of your character. You get some Raiments at the start and some will be unlocked during the game whether you save or sacrifice archenemies and as a reward from getting to a certain point during general story questing and the Avalon Packs. Also, you can unlock different Colors for your Raiments next to the ones you're already given. You can also decide if you want your Raiment with or without Cloak.
Here you can change the characters voice (15).
In this menu you get an overview about the currently unlocked Allies and the 2 you have actually activated for questing in the Avalon Packs. You can also view details on each ally, showing you the spells hes using and their actual affection. The spells your allies use get better the higher their affection is. If on of your allies died or you sacrficed one or both of them, you can also revive them in this menu for a certain amount of lacrima which depends on the grade of appearance, higher grade of appearance results in higher lacrima costs.
In this menu you can change your name. The first Name you are entering is for free, every change afterwards will cost at least 50 lacrima. Your name can consist 12 characters.
When you're entering your satchel, on the left page you can see your currently chosen offerings. On the right page you can find all offerings in your property. You can also upgrade offerings while having at least 2 offerings of the same grade and amount of stars into the next star level. The maximum star level for a spell is 3. Combining 2 star level 3 offerings of the same grade will result in one grade higher star level 0 spell. You are also able to fuse offerings. When entering the fuse menu by pressing "L" you will find the Recepies on the right side (you will learn more and more through playing the quests) and the spell you're currently viewing plus the offerings you have to fuse and you already got.
You can also save different combinations of offerings you carry while pressing "R" in the general satchel menu.
In this menu you get an overview about your right arm whether its divine or dark, your life and magic level and your amount of defense, regeneration and attack. The amount of health is not affected by the life / magic level. You can change your health just by carving several sigils in your right arm.
To change the sigils of your right arm, enter the Carve sigil menu. Here you find the overview about your currently carved sigils and about your character stats (defense, regeneration, attack, health). You can carve a maximum of 5 sigils. 2 sigils into your upper arm (mostly upgrading elements), 2 in your forearm (mostly upgrading the power of offerings) and 1 into your palm (mostly upgrading basic stats).
You can also change the level of your right arm. You can only downgrade life and magic. Downgrading one level costs 20 lacrima and is permanent.
Here you can find an overview of the Black Rites you know, and can change the Black Rite you want to activate by pressing "X" or tapping the screen on the Rite. If you have used your Black Rite in a previous battle, you can pay the cost (with Lacrima) to use it again.
More information can be found here.