The entire book -- including the portions labeled Models of Computation, Director's cut, and Extended Dance Remix -- presents accessible introduction to much of the CS theory landscape.
Someone already praised the shorter book titled "Algorithms" by Dasgupta et al, and I second it. Tim Roughgarden's "Algorithms Illuminated" series is in this genre too.
I'd also recommend the MIT lecture notes on Mathematics for CS: https://courses.csail.mit.edu/6.042/spring18/mcs.pdf This is distinctive for its intuitive explanations with essential, approachable formalism. The exercises are fine too, if you are really mean it.
Sipser's book on the Theory of Computation is great and the one by Hopcroft et al is also very good (as suggested by others). But the most beginner-friendly (or, light on math) coverage of this area is apparently in Peter Linz's book "Introduction to Formal Languages and Automata". An alternative flavor in the treatment of much of the same topics is in this free book: http://cs.brown.edu/people/jsavage/book/