a draw poker player may discard some of his 5 cards and be dealt new ones. the rules say he cannot discard all 5. how many sets of cards can be discarded?

I saw someone answered it online as: This is a problem on combinations. The first answer is 5C4+ (when he discards 4 cards out of 5) + 5C3 (3 out of 5) + 5C2....upto 5C1 which is equal to 30. In addition to this is the case when he does not discard any card at all therefore 1. = 30+1=31

can someone tell me what this means? please help!

Question

a draw poker player may discard some of his 5 cards and be dealt new ones. the rules say he cannot discard all 5. how many sets of cards can be discarded?

I saw someone answered it online as: This is a problem on combinations. The first answer is 5C4+ (when he discards 4 cards out of 5) + 5C3 (3 out of 5) + 5C2....upto 5C1 which is equal to 30. In addition to this is the case when he does not discard any card at all therefore 1. = 30+1=31

can someone tell me what this means? please help!