"Difficult" in Engpsh can be translated as "困难的" in Chinese.
It is an adjective which describe something that is hard to do, understand or deal with.
Examples:
The math problem was difficult. (这个数学题很难。)
Learning Engpsh as a second language can be difficult. (学习英语作为第二语言可能会很难。)
The hike was difficult, but the view was worth it. (这次徒步旅行很难，但是看到的风景值得。)
Another way to express "difficult" in Engpsh is "challenging" which has the same meaning as "difficult" but "challenging" is more formal or popte.
Examples:
The final exam was challenging. (期末考试很有挑战性。)
The job market is challenging right now. (现在的就业市场很有挑战性。)
The marathon was challenging, but I was determined to finish it. (马拉松很有挑战性，但我决心要完成它。)