Use "this" if you're referring to a singular object near you.
Ex.
This is my book.
Use "that" if you're talking about a singular object far from you.
Ex.
I like to use that table.
26 มกราคม 2015
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I don't know about your native language Portuguese, but most Romance languages (Spanish, Italian, French etc) have pronouns equivalent to "this" and "that" in English and which are used in similar ways.