Note the word "often" in Keller's grammar. What ὅδε will refer to depends on the context.
The -δε enclitic is deictic, i.e. it points something out. For example, when Agamemnon insults Achilles to Nestor, he points him out and says:
ἀλλ᾽ ὅδ᾽ ἀνὴρ ἐθέλει περὶ πάντων ἔμμεναι ἄλλων, (Il. 1.287)
But this man (i.e. the man standing right here--you have to picture him pointing Achilles out) wishes to be beyond all others.
When someone is about to provide a list of things or is mentioning that they will speak about a topic/some topics, you can use ὅδε. If they've just finished a list of things, then you use οὗτος.
You see both used in this way frequently in historical writers. For example, Herodotus has:
ταῦτα μὲν Λακεδαιμόνιοι λέγουσι μοῦνοι Ἑλλήνων: τάδε δὲ κατὰ τὰ λεγόμενα ὑπ᾽ Ἑλλήνων ἐγὼ γράφω. (6.53)
These things [i.e. the story he just finished telling] the Lacedaemonians alone of the Greeks report; the following things [i.e. the things he is about to tell] I will write according to the reports of [the rest of the] Greeks.
Where it gets tricky is when someone has said something, and a speaker wishes to resume that thing as a topic. For example, in Plato's Philebus, Socrates picks up on something Philebus has said in the past:
ἀλλὰ γὰρ οἶμαι τόδε λέγεις
But I think this thing you're saying
It continues discussing this thing that Philebus has said. So even if it was mentioned before, it's topical now in their discussion. This is to be contrasted with things, words, etc. in which the speaker is finished.
This is a simple overview of a couple uses, but these demonstratives are quite elastic, and so it would behoove you to read ὅδε's full entry, along with the entries for οὗτος and ἐκεῖνος (which is another demonstrative that indicates remoteness as opposed to nearness) in LSJ and Smyth's grammar (§§ 1238–1261) to get a more nuanced understanding of all the many ways they can be used.
