Thalia is head over heels here, and she does not care who knows it. The whole song is about one thing: a pair of eyes. Ojitos is the cute, diminutive form of ojos (eyes), so "tus ojitos mexicanos" (your little Mexican eyes) sounds tender and a little playful, the way you would talk about someone you adore.
She opens by admitting she wasn't even looking: "Nunca lo busqué, pero por fin lo he encontrado" (I never looked for it, but I finally found it). Then she gets dramatic about looks in general: "Hay miradas que devoran" (there are looks that devour) and "hay miradas que te matan" (there are looks that kill you). His eyes keep drifting to her mouth "como si fuera un tesoro" (as if it were a treasure), and by the second verse she admits she's doing the same thing back.
The chorus is pure gratitude: "Ay, qué suerte, bendita suerte" (oh, what luck, blessed luck). Listen for "No hay tanta vuelta que darle", a handy everyday idiom meaning "there's no need to overthink it". And Cachito (little piece) is a sweet nickname, like calling someone "sweetie". It is a sunny, flirty love song, and it ends with her sure that this kind of love "no se paga con dinero" (can't be paid for with money).