In some ways, the is-ea-id series of pronouns in Latin is something like he-she-it in English (you can even see the ancient Indo-European connection between id and English "it"). At the same time, be careful: these words are used as pronouns far less frequently in Latn than in English! In English, the use of the pronouns "he-she-it" is often required because of the need to have an explicit subject for the verb in English. In Latin, it is perfectly normal for the subject of the verb to be implied, not explicit. So, you only need to use the nominative forms of is-ea-id when you are clarifying some identification that would not be obvious otherwise. A good general piece of advice is: when in doubt, leave them out (especially if you are mentally translating from English, and simply trying to substitute the Latin nominative pronoun for the nominative "he-she-it" in English).
In addition to being used as demonstrative pronouns, these words are also used as demonstrative adjectives, modifying a noun, as in this phrase: ob eam rem, "concerning this thing."
You can also find them compounded, as in the series idem - eadem - idem, meaning "the same."
Here are some examples of today's word in Latin sayings and proverbs; for more information, see the page at the Scala Sapientiae, which contains notes on some of the proverbs cited below, as well as additional proverbs:
id est = i.e.
Erat manus Domini cum eis.
Non semper ea sunt quae videntur.
Cui multum datum est, multum quaeretur ab eo.
Qui petit a te, da ei.
Qui nihil amat, quid ei homini opus vita est?
Id quod volunt, credunt quoque.
Quod video, id credo mihi.
Mens cuiusque is est quisque.
Bene vixit is, qui potuit, cum voluit, mori.
Si tibi parvus equus, tunc parvus erit labor eius.
Sicut mater, ita et filia eius.
Qui bonus est, ab eo bona discito.
Transeunt omnia, et tu cum eis pariter.
Quis eum diligat quem metuat?
Cui prodest scelus, is fecit.
Qui in altum mittit lapidem, super caput eius cadet.
A fructibus eorum cognoscetis eos.
Qui amat divitias, fructus non capiet ex eis.
Qui in gladio occiderit, oportet eum gladio occidi.