You can use Intelligence, instead of Charisma as your spellcasting ability modifier for your warlock spells, warlock class features and eldritch invocations.
Your patron gives you a grimoire called the Book of Shadows, which can be used as a spellcasting focus. Choose two 1st-level spells that have the ritual tag from any class’s spell list. The spells appear in the book and don’t count against the number of spells you know. With your Book of Shadows in hand, you can cast the chosen spells as rituals. You can’t cast the spells except as rituals, unless you’ve learned them by some other means. You can also cast a warlock spell you know as a ritual if it has the ritual tag. On your adventures, you can add other ritual spells to your Book of Shadows. When you find such a spell, you can add it to the book if the spell’s level is equal to or less than half your warlock level (rounded up) and if you can spare the time to transcribe the spell. For each level of the spell, the transcription process takes 2 hours and costs 50 gp for the rare inks needed to inscribe it.
If you lose your Book of Shadows, you can perform a 1-hour ceremony to receive a replacement from your patron. The replacement contains all content that was in the previous book. This ceremony can be performed during a short or long rest, and it destroys the previous book. The book turns to ash when you die.
When you reach 10th level in this class, you deal additional damage with your warlock spells and cantrips equal to your spellcasting ability modifier.