Articles are words that identify and specify a noun, such as "the", "a", and "an".
While English speakers may find it strange not to specify this information, plenty of languages do fine without articles. A comparison is how the Romance languages require the speaker to specify the grammatical gender of every noun, whereas English manages just fine without this feature.
The English word "the" indicates that its noun should already be known from context. Its function is similar to words like "this" and "that", so you might translate "the thing" as ijo ni if necessary.