I would say "join in with the after-school activities" (take part in the after-school activities) You could use 'join' if you are joining a specific club/group. For example "I want to join the after-school painting club" (become a member) A good example I've seen used on here before is: "To join the party" means to become part of the party "To join IN the party" means to take part in the activities of the party.

Charlie is right. "I was upset" is the past simple. So you are talking about a specific time in the past. "I had been upset" is the past perfect, which is used when we are talking about the past and then want to talk about an even earlier time in the past. If we consider these two examples: "When John arrived they went out" (past simple). When John arrived at the house they all went out together. This happens at the same time in the past. "When John arrived, they had gone out" (past perfect). The people had already left the house before John arrived. They went out at an earlier time in the past.

'Have not' is the Present Perfect tense. It is often contracted to 'haven't'. For example, "They haven't been to France". In this tense we are usually talking about an action that happened recently, or about life experiences in general (not at a specific time in the past). 'Do not have' is the Present Simple tense. It is often contracted to 'don't have'. For example, "They don't have any apples". In this tense we use 'have' to talk about possession.

I hope this helps!

If you say "I can watch TV for 2 hours every night" you are saying it's possible to watch TV every night for 2 hours, or that you are allowed to watch TV for 2 hours every night. If you say "I watch TV for 2 hours every night" you are talking about what usually happens/ your habits.

You can't say "I can swim since I was four", you must say "I've been able to swim since I was four". Can we use for ability in the present, what we can do now "I can drive". Could we use for ability in the past, what we could do in the past "I couldn't drive when I was ten". When you say "since I was four", you are talking about a period of time (from when you were four until now). This is the present perfect tense. For the present perfect, future, infinitive and conditional forms you use 'be able to'. "I'll be able to pass the exam soon" (future) You can use 'be able to' for the present simple and past simple, for example "I'm able to drive" or "I wasn't able to drive when I was ten", but it is more formal.

I hope this helps!

This makes sense yes, but I wouldn't use it as a sentence on its own. You could perhaps say: "I usually read from eight until nine" or "My reading time is from eight until nine"