1 Sometimes you can translate '该' into 'it's time to (do sth.)...' For example, 现在咱们该学弟二十四课。 It's time to learn Lesson 24. 你该上床睡觉了。 It's time for you to go to bed. 我该走了。 It's time for me to leave. ("I should leave" is also fine.) 该means 'should', the subject is supposed to do sth. based on good reasons or some regulations,etc. 2 又 here means 'too, also, in addition to some situation..., besides' 我第一次来中国，对于中国又知道的很少。 It's my first time being in China, and also I don't know it well. other examples, 我不舒服，东西又难吃。 I'm not feeling well. Besides, the food is awful.

- in this sentence “该 " means should or ready for something... - "又" means also, besides

现在咱们该学第二十四课。 -> Now we have to study chapter 24 中国的情况又知道的很少。-> I don't know much about condition in China