呐 is a variant of the sentence-final particle 啊 used after words ending in -n. It adds emphasis, encouragement, or a softening tone. Also appears in 呐喊 (nàhǎn, to shout/cry out).
grammar
The particle 啊 changes form based on the preceding sound: 啊 after -a/-e/-i/-o/-u, 呀 after -a/-o/-e, 哇 after -u/-ao, 呐 after -n. In practice, many speakers just write 啊.
