Ritual Caster Feat

[Ranikirn.]

You have learned a number o f spells that you can cast as
rituals. These spells are written in a ritual book, which
you must have in hand while casting one o f them.
When you choose this feat, you acquire a ritual book
holding two 1st-level spells o f your choice. Choose one
o f the following classes: bard, cleric, druid, sorcerer,
warlock, or wizard. You must choose your spells
from that class’s spell list, and the spells you choose
must have the ritual tag. The class you choose also
determines your spellcasting ability for these spells:
Charisma for bard, sorcerer, or warlock; Wisdom for
cleric or druid; or Intelligence for wizard.
If you come across a spell in written form, such as a
magical spell scroll or a w izard’s spellbook, you might
be able to add it to your ritual book. The spell must be
on the spell list for the class you chose, the spell’s level
can be no higher than half your level (rounded up), and
it must have the ritual tag. The process o f copying the
spell into your ritual book takes 2 hours per level o f the
spell, and costs 50 gp per level. The cost represents
material components you expend as you experiment
with the spell to master it, as well as the fine inks you
need to record it.

My doubt is: I must prepare these spells or i can cast it (as rituals obviously) even if I didn't prepared them?

[PhoenixPhyre]

You have learned a number o f spells that you can cast as
rituals. These spells are written in a ritual book, which
you must have in hand while casting one o f them.
When you choose this feat, you acquire a ritual book
holding two 1st-level spells o f your choice. Choose one
o f the following classes: bard, cleric, druid, sorcerer,
warlock, or wizard. You must choose your spells
from that class’s spell list, and the spells you choose
must have the ritual tag. The class you choose also
determines your spellcasting ability for these spells:
Charisma for bard, sorcerer, or warlock; Wisdom for
cleric or druid; or Intelligence for wizard.
If you come across a spell in written form, such as a
magical spell scroll or a w izard’s spellbook, you might
be able to add it to your ritual book. The spell must be
on the spell list for the class you chose, the spell’s level
can be no higher than half your level (rounded up), and
it must have the ritual tag. The process o f copying the
spell into your ritual book takes 2 hours per level o f the
spell, and costs 50 gp per level. The cost represents
material components you expend as you experiment
with the spell to master it, as well as the fine inks you
need to record it.

My doubt is: I must prepare these spells or i can cast it (as rituals obviously) even if I didn't prepared them?

You can't prepare them (unless you pick a spell that you could otherwise prepare). They're completely separate from your normal casting and can only be cast as rituals.

[leogobsin]

Ritual Caster doesn't require any preparation, no. If the spell's in your ritual book, you can cast it as a ritual any time.

[Anymage]

The wizard and tomelocks are the only other classes that have a spellbook or similar mechanic. Wizards can explicitly cast rituals out of their spellbooks even if they haven't prepared the spell, and the relevant tomelock invocation strongly implies as much as well.

Nothing in the feat implies that you could prepare spells anyways, or gives any number of slots available. Even if said slots were only used to know what spells could be used as rituals today. As such, I think it's safe to say that any spell in your book can be freely cast as a ritual, so long as you have the time and components handy.

[Ranikirn.]

Now it's clearer, thanks all of you.