Augustine, naming, pointing
The quote from Augustine's Confessions introduces a concept that will recur in the early Remarks: ostensive teaching of language, in which a teacher directs a pupil's attention to some object - typically by pointing to it - while simultaneously uttering a sound. Augustine recounts that as a child he surmised that such pointing was intended to establish a relationship between the specific sound uttered and the specific object to which the teacher was pointing.
The first paragraph of this Remark introduces two concepts that are central to the early Remarks. One is the role of words in a language. And from Augustine's quote Wittgenstein infers that Augustine views that role as being to "name" the object to which the teacher is pointing. In somewhat the same way as the teacher points to an object, the name "points" to it as well. Or does the name "point" to the type of object of which the specific object is an instance? Or to some feature of the object, eg, its shape or color? Or to the object as an example of the concept "1"? Each of these possibilities is explored in the next few dozen Remarks.
five red apples
On a first reading it's easy to miss (at least it was for me) the full significance of the description of a trip to the market with a piece of paper on which is inscribed simply "five red apples". The shopkeeper fills the (presumed) order as follows. He finds a drawer labeled "apples" and opens it. He then searches a chart of labeled color samples for the sample labeled "red". Finally, he removes apples of that color from the opened drawer while reciting the sequence of integers - one for each apple removed - until reaching "five".
We tend to think of the ability to understand language as being a hallmark of cognition. But where in this mechanical process (that one can easily imagine automating) is cognition? In fact, where is language? In the original German, the inscription on the piece of paper is referred to as "Zeichen", which translates as "signs", "symbols", or simply "marks". And if you reread the description of the shopkeeper's procedure thinking not of familiar words but of arbitrarily chosen marks (think contemporary scan codes), the concepts of language, word, and meaning seem to be missing.
But are they? We tend to think of the function of language as being to facilitate communication - the transfer of information. But what about commands? Their express purpose is to get the hearer to act - to do something. And that idea can be generalized to the purpose of language being to alter behavior. In particular, a speaker intends that an utterance cause a hearer to act, and the meaning of the utterance can be viewed as being the intended action.
From that perspective, "five red apples" - or even "***** O Ѽ" - counts as a "sentence" in a language game as long as the shopkeeper acts as intended by the inscriber. Perhaps that is what W had in mind when writing "I assume [the shopkeeper] acts as I have described", ie, his actions have meaning in the described context.