"Introduction to the Theory of Computation" (by Michael Sipser) is a perfect book for TCS beginners. It is superbly accessible and friendly to TCS rookies, which never makes your bored during your
reading. I never regret devoting time & energy to reading it - I'm still at the beginning of my journey with it..
Ch. 0 Introduction - on several very basic maths basis that is the premise of continuing your study;
Ch. 1 Regular Language - Staring with regular expression that every CSer knows about, author elaborates Finite Automata, DFA\(G)NFA with a extremely accessible way to explanation, including their properties, conversions among each other.
What's more, everything is guarded by rigorous MATHS proofs, so you would have fun concisely, without any theoretical rigor loss. The JOY of this chapter is: FA is a fun toy, it is flexible but follows precise rules of Maths. 
Seriously, can't wait to read on !