You might remember the meaning of the character 纳 with this easy mnemonic:
A silk (纟) factory worker accepted a big delivery and left the box in the storage room. But it tumbled over by itself and from the down box (冂) a man (人) emerged. The man was a spy who entered (入) to investigate.
Using mnemonics to remember the meaning of Chinese characters like has a huge impact on how long to learn Mandarin it takes.