Translation:Shulchan Aruch/Orach Chaim/101
Paragraph 1: One who prays needs to concentrate while saying all Berachos. However, if one is not able to concentrate during prayers, one must (at least) pray during the Avos. If one did not concentrate during the Avos, even if they concentrated during the rest of the prayers, they are obligated to return and pray. Ramah: Nowadays, we do not return and pray because we do not have “real kavanah”, so if (he did), why should he go back (and pray)?
Paragraph 2: One should not pray just in his heart (without saying the words) but one must actually say them with his mouth