Erken is a verb. It means to admit, to acknowledge, or to recognize, depending on context.
In this sentence, it means to admit.
A useful thing to know is that Afrikaans verbs usually do not change form for different subjects in the present tense:
So unlike English, Afrikaans does not add an extra -s for he.
Moeg is an adjective meaning tired.
In this sentence, it comes after the subject and works with is:
Afrikaans adjectives used after a linking verb like is usually do not change form. So moeg stays moeg.
Sometimes, especially in less formal speech, Afrikaans may leave out dat after certain verbs. But for learners, it is best to keep it until you are comfortable with the pattern.
So this sentence is very safe and standard:
If dat is omitted in informal usage, the word order can still follow subordinate-clause patterns depending on the construction, so it is better not to guess too early as a learner.
The pattern is:
So here:
A simple formula for this sentence is:
Hy erken + dat + hy + moeg + is
A common negative version would be:
Afrikaans usually uses double negation with nie ... nie.
Inside the subordinate clause:
You could also negate the main clause instead:
That means He does not admit that he is tired. The place of nie depends on what exactly you are negating.