"to correctly pronounce any Finnish word you just string together the sounds of the letters of the word."

This is a lie-to-children that I too was taught in school, but it's not even remotely true. Consider:

herne(k)keitto leu(v)an rei(j)än isän (=m)maa sydäm(m)en

You'd sound like a robot if you just pronounced them "as written". Computer phonetic analysis of the language reveals even more patterns where the written language indisputably deviates from the spoken one, but these at least should be easy to verify without specialist knowledge or equipment.

Here's a long but relatively easy-to-follow article on the subject http://www.cs.tut.fi/~jkorpela/orto.html (in Finnish).