grammar.adjectives.demonstratives
Este, ese, aquel before nouns
Three distances agreeing with the noun: este libro, esa mesa, aquellos años. Ese also covers 'near you' and the recently mentioned.
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Explanation
Demonstrative adjectives go before the noun and mark three distances, agreeing in gender and number: este/esta/estos/estas (near the speaker (este libro), ese/esa/esos/esas (near the listener or just mentioned) esa mesa), aquel/aquella/aquellos/aquellas (far from both, in space or time, aquellos años).
Ese covers a lot of ground: things near the person you're talking to, and things recently brought up in the conversation. Aquel adds distance, often nostalgic or remote: aquella época, aquel verano.
Position affects tone. Before the noun they're neutral (ese modelo); placed after the noun (which then needs the article too) they often sound dismissive: el tipo ese ('that guy'), la idea esa. In time expressions: esta semana, ese día ('the day in question'), aquella vez.
Examples
How much does that model cost?
Region: global
Those years (back then) were hard.
Region: global
This proposal convinces me more than that one.